Re-named the "case" macro to "when".

27 files changed, 250 insertions, 250 deletions

diff --git a/stdlib/source/library/lux/data/bit.lux b/stdlib/source/library/lux/data/bit.lux
index dcb0ad6bb..18b53bb1c 100644
--- a/stdlib/source/library/lux/data/bit.lux
+++ b/stdlib/source/library/lux/data/bit.lux
@@ -31,7 +31,7 @@
    (def equivalence ..equivalence)
    
    (def (hash value)
-     (case value
+     (when value
        #0 2
        #1 3))))
 
@@ -55,7 +55,7 @@
        "#0"))
 
    (def (decoded input)
-     (case input
+     (when input
        "#1" {.#Right #1}
        "#0" {.#Right #0}
        _    {.#Left "Wrong syntax for Bit."}))))
diff --git a/stdlib/source/library/lux/data/collection/bits.lux b/stdlib/source/library/lux/data/collection/bits.lux
index b036bb9dc..1e84ee9c4 100644
--- a/stdlib/source/library/lux/data/collection/bits.lux
+++ b/stdlib/source/library/lux/data/collection/bits.lux
@@ -69,7 +69,7 @@
                      output ..empty])
          (let [idx|output (-- size|output)]
            (if (n.> 0 size|output)
-             (case (|> (..chunk idx|output input)
+             (when (|> (..chunk idx|output input)
                        (pipe.cond [(pipe.new (n.= chunk_index idx|output) [])]
                                   [(<op> bit_index)]
 
@@ -109,7 +109,7 @@
 
 (def .public (not input)
   (-> Bits Bits)
-  (case (array.size input)
+  (when (array.size input)
     0
     ..empty
 
@@ -117,7 +117,7 @@
     (loop (again [size|output size|output
                   output ..empty])
       (let [idx (-- size|output)]
-        (case (|> input (..chunk idx) i64.not .nat)
+        (when (|> input (..chunk idx) i64.not .nat)
           0
           (again (-- size|output) output)
 
@@ -133,7 +133,7 @@
 (with_template [<name> <op>]
   [(def .public (<name> param subject)
      (-> Bits Bits Bits)
-     (case (n.max (array.size param)
+     (when (n.max (array.size param)
                   (array.size subject))
        0
        ..empty
@@ -143,7 +143,7 @@
                      output ..empty])
          (let [idx (-- size|output)]
            (if (n.> 0 size|output)
-             (case (|> (..chunk idx subject)
+             (when (|> (..chunk idx subject)
                        (<op> (..chunk idx param))
                        .nat)
                0
diff --git a/stdlib/source/library/lux/data/collection/dictionary.lux b/stdlib/source/library/lux/data/collection/dictionary.lux
index 99badd2bc..a2e1282d5 100644
--- a/stdlib/source/library/lux/data/collection/dictionary.lux
+++ b/stdlib/source/library/lux/data/collection/dictionary.lux
@@ -271,7 +271,7 @@
                              (if (with_bit_position? (to_bit_position hierarchy_idx)
                                    bitmap)
                                [(++ base_idx)
-                                (case (array.item base_idx base)
+                                (when (array.item base_idx base)
                                   {.#Left sub_node}
                                   (array.has! hierarchy_idx sub_node h_array)
 
@@ -289,7 +289,7 @@
 ... So, this test is introduced to detect them.
 (def (node#empty? node)
   (All (_ k v) (-> (Node k v) Bit))
-  (case node
+  (when node
     {#Base ..clean_bitmap _}
     true
 
@@ -298,7 +298,7 @@
 
 (def (node#has level hash key val key_hash node)
   (All (_ k v) (-> Level Hash_Code k v (Hash k) (Node k v) (Node k v)))
-  (case node
+  (when node
     ... For #Hierarchy nodes, check whether one can add the element to
     ... a sub-node. If impossible, introduce a new singleton sub-node.
     {#Hierarchy _size hierarchy}
@@ -317,7 +317,7 @@
       (if (with_bit_position? bit bitmap)
         ... If so...
         (let [idx (base_index bit bitmap)]
-          {#Base bitmap (case (array.item idx base)
+          {#Base bitmap (when (array.item idx base)
                           ... If it's being used by a node, add the KV to it.
                           {.#Left sub_node}
                           (let [sub_node' (node#has (level_up level) hash key val key_hash sub_node)]
@@ -371,7 +371,7 @@
     (if (n.= hash _hash)
       ... If they're equal, that means the new KV contributes to the
       ... collisions.
-      (case (collision_index key_hash key _colls)
+      (when (collision_index key_hash key _colls)
         ... If the key was already present in the collisions-list, its
         ... value gets updated.
         {.#Some coll_idx}
@@ -390,7 +390,7 @@
 
 (def (node#lacks level hash key key_hash node)
   (All (_ k v) (-> Level Hash_Code k (Hash k) (Node k v) (Node k v)))
-  (case node
+  (when node
     ... For #Hierarchy nodes, find out if there's a valid sub-node for
     ... the Hash-Code.
     {#Hierarchy h_size h_array}
@@ -422,7 +422,7 @@
     (let [bit (level_bit_position level hash)]
       (if (with_bit_position? bit bitmap)
         (let [idx (base_index bit bitmap)]
-          (case (array.item idx base)
+          (when (array.item idx base)
             ... If set, check if it's a sub_node, and remove the KV
             ... from it.
             {.#Left sub_node}
@@ -460,7 +460,7 @@
 
     ... For #Collisions nodes, It need to find out if the key already existst.
     {#Collisions _hash _colls}
-    (case (collision_index key_hash key _colls)
+    (when (collision_index key_hash key _colls)
       ... If not, then there's nothing to remove.
       {.#None}
       node
@@ -477,7 +477,7 @@
 
 (def (node#value level hash key key_hash node)
   (All (_ k v) (-> Level Hash_Code k (Hash k) (Node k v) (Maybe v)))
-  (case node
+  (when node
     ... For #Hierarchy nodes, just look-up the key on its children.
     {#Hierarchy _size hierarchy}
     (let [index (level_index level hash)]
@@ -489,7 +489,7 @@
     {#Base bitmap base}
     (let [bit (level_bit_position level hash)]
       (if (with_bit_position? bit bitmap)
-        (case (array.item (base_index bit bitmap) base)
+        (when (array.item (base_index bit bitmap) base)
           {.#Left sub_node}
           (node#value (level_up level) hash key key_hash sub_node)
 
@@ -508,7 +508,7 @@
 
 (def (node#size node)
   (All (_ k v) (-> (Node k v) Nat))
-  (case node
+  (when node
     {#Hierarchy _size hierarchy}
     (array.mix (function (_ _ item total)
                  (n.+ item total))
@@ -520,7 +520,7 @@
                  (n.+ item total))
                0
                (array.each (function (_ sub_node')
-                             (case sub_node'
+                             (when sub_node'
                                {.#Left sub_node} (node#size sub_node)
                                {.#Right _}       1))
                            base))
@@ -531,7 +531,7 @@
 
 (def (node#mix f init node)
   (All (_ k v a) (-> (-> [k v] a a) a (Node k v) a))
-  (case node
+  (when node
     {#Hierarchy _size hierarchy}
     (array.mix (function (_ _ sub_node current)
                  (node#mix f current sub_node))
@@ -540,7 +540,7 @@
 
     {#Base bitmap base}
     (array.mix (function (_ _ branch current)
-                 (case branch
+                 (when branch
                    {.#Left sub_node}
                    (node#mix f current sub_node)
 
@@ -592,7 +592,7 @@
 
 (def .public (key? dict key)
   (All (_ k v) (-> (Dictionary k v) k Bit))
-  (case (value key dict)
+  (when (value key dict)
     {.#None}
     false
     
@@ -603,13 +603,13 @@
 
 (def .public (has' key val dict)
   (All (_ k v) (-> k v (Dictionary k v) (Try (Dictionary k v))))
-  (case (value key dict)
+  (when (value key dict)
     {.#None}   {try.#Success (has key val dict)}
     {.#Some _} (exception.except ..key_already_exists [])))
 
 (def .public (revised key f dict)
   (All (_ k v) (-> k (-> v v) (Dictionary k v) (Dictionary k v)))
-  (case (value key dict)
+  (when (value key dict)
     {.#None}
     dict
 
@@ -664,7 +664,7 @@
 (def .public (composite_with f dict2 dict1)
   (All (_ k v) (-> (-> v v v) (Dictionary k v) (Dictionary k v) (Dictionary k v)))
   (node#mix (function (_ [key val2] dict)
-              (case (value key dict)
+              (when (value key dict)
                 {.#None}
                 (has key val2 dict)
 
@@ -675,7 +675,7 @@
 
 (def .public (re_bound from_key to_key dict)
   (All (_ k v) (-> k k (Dictionary k v) (Dictionary k v)))
-  (case (value from_key dict)
+  (when (value from_key dict)
     {.#None}
     dict
 
@@ -688,7 +688,7 @@
   (All (_ k v) (-> (List k) (Dictionary k v) (Dictionary k v)))
   (let [[key_hash _] dict]
     (list#mix (function (_ key new_dict)
-                (case (value key dict)
+                (when (value key dict)
                   {.#None}     new_dict
                   {.#Some val} (has key val new_dict)))
               (empty key_hash)
@@ -701,7 +701,7 @@
      (and (n.= (..size reference)
                (..size subject))
           (list.every? (function (_ [k rv])
-                         (case (..value k subject)
+                         (when (..value k subject)
                            {.#Some sv}
                            (,#= rv sv)
 
@@ -713,13 +713,13 @@
   (All (_ k) (Functor (Node k)))
   (implementation
    (def (each f fa)
-     (case fa
+     (when fa
        {#Hierarchy size hierarchy}
        {#Hierarchy size (array.each (each f) hierarchy)}
        
        {#Base bitmap base}
        {#Base bitmap (array.each (function (_ either)
-                                   (case either
+                                   (when either
                                      {.#Left fa'}
                                      {.#Left (each f fa')}
                                      
diff --git a/stdlib/source/library/lux/data/collection/dictionary/ordered.lux b/stdlib/source/library/lux/data/collection/dictionary/ordered.lux
index 44848eae6..3541cef42 100644
--- a/stdlib/source/library/lux/data/collection/dictionary/ordered.lux
+++ b/stdlib/source/library/lux/data/collection/dictionary/ordered.lux
@@ -64,7 +64,7 @@
   (let [... (open "_#[0]") (the #order dict)
         ]
     (loop (again [node (the #root dict)])
-      (case node
+      (when node
         {.#None}
         {.#None}
 
@@ -89,7 +89,7 @@
   (let [... (open "_#[0]") (the #order dict)
         ]
     (loop (again [node (the #root dict)])
-      (case node
+      (when node
         {.#None}
         false
 
@@ -105,13 +105,13 @@
 (with_template [<name> <side>]
   [(def .public (<name> dict)
      (All (_ k v) (-> (Dictionary k v) (Maybe v)))
-     (case (the #root dict)
+     (when (the #root dict)
        {.#None}
        {.#None}
 
        {.#Some node}
        (loop (again [node node])
-         (case (the <side> node)
+         (when (the <side> node)
            {.#None}
            {.#Some (the #value node)}
 
@@ -125,7 +125,7 @@
 (def .public (size dict)
   (All (_ k v) (-> (Dictionary k v) Nat))
   (loop (again [node (the #root dict)])
-    (case node
+    (when node
       {.#None}
       0
 
@@ -140,7 +140,7 @@
 (with_template [<name> <other_color> <self_color> <no_change>]
   [(def (<name> self)
      (All (_ k v) (-> (Node k v) (Node k v)))
-     (case (the #color self)
+     (when (the #color self)
        {<other_color>}
        (.has #color {<self_color>} self)
 
@@ -154,7 +154,7 @@
 
 (def (with_left addition center)
   (All (_ k v) (-> (Node k v) (Node k v) (Node k v)))
-  (case (the #color center)
+  (when (the #color center)
     {#Red}
     (red (the #key center)
          (the #value center)
@@ -167,9 +167,9 @@
                                         (the #value center)
                                         {.#Some addition}
                                         (the #right center)))]
-      (case (the #color addition)
+      (when (the #color addition)
         {#Red}
-        (case (the #left addition)
+        (when (the #left addition)
           (^.multi {.#Some left}
                    [(the #color left) {#Red}])
           (red (the #key addition)
@@ -181,7 +181,7 @@
                               (the #right center))})
 
           _
-          (case (the #right addition)
+          (when (the #right addition)
             (^.multi {.#Some right}
                      [(the #color right) {#Red}])
             (red (the #key right)
@@ -203,7 +203,7 @@
 
 (def (with_right addition center)
   (All (_ k v) (-> (Node k v) (Node k v) (Node k v)))
-  (case (the #color center)
+  (when (the #color center)
     {#Red}
     (red (the #key center)
          (the #value center)
@@ -216,9 +216,9 @@
                                         (the #value center)
                                         (the #left center)
                                         {.#Some addition}))]
-      (case (the #color addition)
+      (when (the #color addition)
         {#Red}
-        (case (the #right addition)
+        (when (the #right addition)
           (^.multi {.#Some right}
                    [(the #color right) {#Red}])
           (red (the #key addition)
@@ -230,7 +230,7 @@
                {.#Some (blackened right)})
 
           _
-          (case (the #left addition)
+          (when (the #left addition)
             (^.multi {.#Some left}
                      [(the #color left) {#Red}])
             (red (the #key left)
@@ -254,7 +254,7 @@
   (All (_ k v) (-> k v (Dictionary k v) (Dictionary k v)))
   (let [(open "_#[0]") (the #order dict)
         root' (loop (again [?root (the #root dict)])
-                (case ?root
+                (when ?root
                   {.#None}
                   {.#Some (red key value {.#None} {.#None})}
 
@@ -281,7 +281,7 @@
 
 (def (left_balanced key value ?left ?right)
   (All (_ k v) (-> k v (Maybe (Node k v)) (Maybe (Node k v)) (Node k v)))
-  (case ?left
+  (when ?left
     (^.multi {.#Some left}
              [(the #color left) {#Red}]
              [(the #left left) {.#Some left>>left}]
@@ -310,7 +310,7 @@
 
 (def (right_balanced key value ?left ?right)
   (All (_ k v) (-> k v (Maybe (Node k v)) (Maybe (Node k v)) (Node k v)))
-  (case ?right
+  (when ?right
     (^.multi {.#Some right}
              [(the #color right) {#Red}]
              [(the #right right) {.#Some right>>right}]
@@ -337,13 +337,13 @@
 
 (def (without_left key value ?left ?right)
   (All (_ k v) (-> k v (Maybe (Node k v)) (Maybe (Node k v)) (Node k v)))
-  (case ?left
+  (when ?left
     (^.multi {.#Some left}
              [(the #color left) {#Red}])
     (red key value {.#Some (blackened left)} ?right)
 
     _
-    (case ?right
+    (when ?right
       (^.multi {.#Some right}
                [(the #color right) {#Black}])
       (right_balanced key value ?left {.#Some (reddened right)})
@@ -366,13 +366,13 @@
 
 (def (without_right key value ?left ?right)
   (All (_ k v) (-> k v (Maybe (Node k v)) (Maybe (Node k v)) (Node k v)))
-  (case ?right
+  (when ?right
     (^.multi {.#Some right}
              [(the #color right) {#Red}])
     (red key value ?left {.#Some (blackened right)})
 
     _
-    (case ?left
+    (when ?left
       (^.multi {.#Some left}
                [(the #color left) {#Black}])
       (left_balanced key value {.#Some (reddened left)} ?right)
@@ -395,7 +395,7 @@
 
 (def (prepended ?left ?right)
   (All (_ k v) (-> (Maybe (Node k v)) (Maybe (Node k v)) (Maybe (Node k v))))
-  (case [?left ?right]
+  (when [?left ?right]
     [{.#None} _]
     ?right
 
@@ -403,11 +403,11 @@
     ?left
 
     [{.#Some left} {.#Some right}]
-    (case [(the #color left) (the #color right)]
+    (when [(the #color left) (the #color right)]
       [{#Red} {#Red}]
       (do maybe.monad
         [fused (prepended (the #right left) (the #right right))]
-        (case (the #color fused)
+        (when (the #color fused)
           {#Red}
           (in (red (the #key fused)
                    (the #value fused)
@@ -446,7 +446,7 @@
       [{#Black} {#Black}]
       (do maybe.monad
         [fused (prepended (the #right left) (the #left right))]
-        (case (the #color fused)
+        (when (the #color fused)
           {#Red}
           (in (red (the #key fused)
                    (the #value fused)
@@ -477,7 +477,7 @@
   (All (_ k v) (-> k (Dictionary k v) (Dictionary k v)))
   (let [(open "_#[0]") (the #order dict)
         [?root found?] (loop (again [?root (the #root dict)])
-                         (case ?root
+                         (when ?root
                            {.#Some root}
                            (let [root_key (the #key root)
                                  root_val (the #value root)]
@@ -486,7 +486,7 @@
                                            (the #right root))
                                 true]
                                (let [go_left? (_#< root_key key)]
-                                 (case (again (if go_left?
+                                 (when (again (if go_left?
                                                 (the #left root)
                                                 (the #right root)))
                                    [{.#None} .false]
@@ -494,7 +494,7 @@
 
                                    [side_outcome _]
                                    (if go_left?
-                                     (case (the #left root)
+                                     (when (the #left root)
                                        (^.multi {.#Some left}
                                                 [(the #color left) {#Black}])
                                        [{.#Some (without_left root_key root_val side_outcome (the #right root))}
@@ -503,7 +503,7 @@
                                        _
                                        [{.#Some (red root_key root_val side_outcome (the #right root))}
                                         false])
-                                     (case (the #right root)
+                                     (when (the #right root)
                                        (^.multi {.#Some right}
                                                 [(the #color right) {#Black}])
                                        [{.#Some (without_right root_key root_val (the #left root) side_outcome)}
@@ -518,7 +518,7 @@
                            {.#None}
                            [{.#None} false]
                            ))]
-    (case ?root
+    (when ?root
       {.#None}
       (if found?
         (.has #root ?root dict)
@@ -530,7 +530,7 @@
 
 (def .public (revised key transform dict)
   (All (_ k v) (-> k (-> v v) (Dictionary k v) (Dictionary k v)))
-  (case (..value key dict)
+  (when (..value key dict)
     {.#Some old}
     (..has key (transform old) dict)
 
@@ -548,7 +548,7 @@
   [(def .public (<name> dict)
      (All (_ k v) (-> (Dictionary k v) (List <type>)))
      (loop (again [node (the #root dict)])
-       (case node
+       (when node
          {.#None}
          (list)
 
@@ -570,7 +570,7 @@
      (let [(open "/#[0]") (the #order reference)]
        (loop (again [entriesR (entries reference)
                      entriesS (entries sample)])
-         (case [entriesR entriesS]
+         (when [entriesR entriesS]
            [{.#End} {.#End}]
            true
 
diff --git a/stdlib/source/library/lux/data/collection/list.lux b/stdlib/source/library/lux/data/collection/list.lux
index 4114acd8e..c2dff94fc 100644
--- a/stdlib/source/library/lux/data/collection/list.lux
+++ b/stdlib/source/library/lux/data/collection/list.lux
@@ -1,6 +1,6 @@
 (.require
  [library
-  [lux (.except revised all only with)
+  [lux (.except revised all only with when)
    [abstract
     [monoid (.only Monoid)]
     [apply (.only Apply)]
@@ -30,7 +30,7 @@
   (Mix List)
   (implementation
    (def (mix f init xs)
-     (case xs
+     (.when xs
        {.#End}
        init
 
@@ -39,7 +39,7 @@
 
 (def .public (mixes f init inputs)
   (All (_ a b) (-> (-> a b b) b (List a) (List b)))
-  (case inputs
+  (.when inputs
     {.#End}
     (list init)
     
@@ -57,7 +57,7 @@
 (def .public (only keep? xs)
   (All (_ a)
     (-> (Predicate a) (List a) (List a)))
-  (case xs
+  (.when xs
     {.#End}
     {.#End}
     
@@ -68,7 +68,7 @@
 
 (def .public (partition satisfies? list)
   (All (_ a) (-> (Predicate a) (List a) [(List a) (List a)]))
-  (case list
+  (.when list
     {.#End}
     [{.#End} {.#End}]
 
@@ -85,7 +85,7 @@
 
 (def .public partial
   (macro (_ tokens state)
-    (case (reversed tokens)
+    (.when (reversed tokens)
       {.#Item tail heads}
       {.#Right [state (list (..mix (function (_ head tail)
                                      (` {.#Item (, head) (, tail)}))
@@ -97,9 +97,9 @@
 
 (def .public (pairs xs)
   (All (_ a) (-> (List a) (Maybe (List [a a]))))
-  (case xs
+  (.when xs
     (partial x1 x2 xs')
-    (case (pairs xs')
+    (.when (pairs xs')
       {.#Some tail}
       {.#Some (partial [x1 x2] tail)}
 
@@ -117,7 +117,7 @@
      (All (_ a)
        (-> Nat (List a) (List a)))
      (if (n.> 0 n)
-       (case xs
+       (.when xs
          {.#End}
          {.#End}
          
@@ -133,7 +133,7 @@
   [(def .public (<name> predicate xs)
      (All (_ a)
        (-> (Predicate a) (List a) (List a)))
-     (case xs
+     (.when xs
        {.#End}
        {.#End}
        
@@ -149,9 +149,9 @@
 (def .public (split_at n xs)
   (All (_ a)
     (-> Nat (List a) [(List a) (List a)]))
-  (case n
+  (.when n
     0 [{.#End} xs]
-    _ (case xs
+    _ (.when xs
         {.#End}
         [{.#End} {.#End}]
         
@@ -162,7 +162,7 @@
 (def (split_when' predicate ys xs)
   (All (_ a)
     (-> (Predicate a) (List a) (List a) [(List a) (List a)]))
-  (case xs
+  (.when xs
     {.#End}
     [ys xs]
 
@@ -179,7 +179,7 @@
 
 (def .public (sub size list)
   (All (_ a) (-> Nat (List a) (List (List a))))
-  (case list
+  (.when list
     {.#End}
     {.#End}
 
@@ -190,14 +190,14 @@
 (def .public (repeated n x)
   (All (_ a)
     (-> Nat a (List a)))
-  (case n
+  (.when n
     0 {.#End}
     _ {.#Item x (repeated (-- n) x)}))
 
 (def (iterations' f x)
   (All (_ a)
     (-> (-> a (Maybe a)) a (List a)))
-  (case (f x)
+  (.when (f x)
     {.#Some x'}
     {.#Item x (iterations' f x')}
 
@@ -207,7 +207,7 @@
 (def .public (iterations f x)
   (All (_ a)
     (-> (-> a (Maybe a)) a (List a)))
-  (case (f x)
+  (.when (f x)
     {.#Some x'}
     {.#Item x (iterations' f x')}
 
@@ -217,12 +217,12 @@
 (def .public (one check xs)
   (All (_ a b)
     (-> (-> a (Maybe b)) (List a) (Maybe b)))
-  (case xs
+  (.when xs
     {.#End}
     {.#None}
 
     {.#Item x xs'}
-    (case (check x)
+    (.when (check x)
       {.#Some output}
       {.#Some output}
       
@@ -235,7 +235,7 @@
   (for @.js
        ... TODO: Stop relying on this ASAP.
        (mix (function (_ head tail)
-              (case (check head)
+              (.when (check head)
                 {.#Some head}
                 {.#Item head tail}
                 
@@ -243,12 +243,12 @@
                 tail))
             {.#End}
             (reversed xs))
-       (case xs
+       (.when xs
          {.#End}
          {.#End}
 
          {.#Item x xs'}
-         (case (check x)
+         (.when (check x)
            {.#Some output}
            {.#Item output (all check xs')}
            
@@ -267,7 +267,7 @@
 (def .public (interposed sep xs)
   (All (_ a)
     (-> a (List a) (List a)))
-  (case xs
+  (.when xs
     {.#End}
     xs
 
@@ -285,7 +285,7 @@
   [(def .public (<name> predicate items)
      (All (_ a)
        (-> (Predicate a) (List a) Bit))
-     (case items
+     (.when items
        {.#End}
        <init>
 
@@ -300,12 +300,12 @@
 (def .public (item i xs)
   (All (_ a)
     (-> Nat (List a) (Maybe a)))
-  (case xs
+  (.when xs
     {.#End}
     {.#None}
 
     {.#Item x xs'}
-    (case i
+    (.when i
       0 {.#Some x}
       _ (item (-- i) xs'))))
 
@@ -313,7 +313,7 @@
   (All (_ a) (-> (Equivalence a) (Equivalence (List a))))
   (implementation
    (def (= xs ys)
-     (case [xs ys]
+     (.when [xs ys]
        [{.#End} {.#End}]
        true
 
@@ -342,7 +342,7 @@
    (def identity
      {.#End})
    (def (composite xs ys)
-     (case xs
+     (.when xs
        {.#End}
        ys
        
@@ -355,7 +355,7 @@
   (Functor List)
   (implementation
    (def (each f ma)
-     (case ma
+     (.when ma
        {.#End}
        {.#End}
        
@@ -370,7 +370,7 @@
    (def functor ..functor)
 
    (def (on fa ff)
-     (case ff
+     (.when ff
        {.#End}
        {.#End}
        
@@ -392,7 +392,7 @@
 
 (def .public (sorted < xs)
   (All (_ a) (-> (-> a a Bit) (List a) (List a)))
-  (case xs
+  (.when xs
     {.#End}
     (list)
     
@@ -410,7 +410,7 @@
 
 (def .public (empty? xs)
   (All (_ a) (Predicate (List a)))
-  (case xs
+  (.when xs
     {.#End}
     true
     
@@ -419,7 +419,7 @@
 
 (def .public (member? eq xs x)
   (All (_ a) (-> (Equivalence a) (List a) a Bit))
-  (case xs
+  (.when xs
     {.#End}
     false
     
@@ -430,7 +430,7 @@
 (with_template [<name> <output> <side>]
   [(def .public (<name> xs)
      (All (_ a) (-> (List a) (Maybe <output>)))
-     (case xs
+     (.when xs
        {.#End}
        {.#None}
 
@@ -443,7 +443,7 @@
 
 (def .public (indices size)
   (All (_ a) (-> Nat (List Nat)))
-  (case size
+  (.when size
     0 (list)
     _ (|> size -- (enum.range n.enum 0))))
 
@@ -455,7 +455,7 @@
   (-> Nat Text)
   (loop (again [input value
                 output ""])
-    (let [digit (case (n.% 10 input)
+    (let [digit (.when (n.% 10 input)
                   0 "0"
                   1 "1"
                   2 "2"
@@ -469,13 +469,13 @@
                   _ (undefined))
           output' ("lux text concat" digit output)
           input' (n./ 10 input)]
-      (case input'
+      (.when input'
         0 output'
         _ (again input' output')))))
 
 (def .public zipped
   (macro (_ tokens state)
-    (case tokens
+    (.when tokens
       (list [_ {.#Nat num_lists}])
       (if (n.> 0 num_lists)
         (let [(open "[0]") ..functor
@@ -498,7 +498,7 @@
               list_vars (each product.right vars+lists)
               code (` (is (, zipped_type)
                           (function ((, g!step) (,* list_vars))
-                            (case [(,* list_vars)]
+                            (.when [(,* list_vars)]
                               (, pattern)
                               {.#Item [(,* (each product.left vars+lists))]
                                       ((, g!step) (,* list_vars))}
@@ -516,7 +516,7 @@
 
 (def .public zipped_with
   (macro (_ tokens state)
-    (case tokens
+    (.when tokens
       (list [_ {.#Nat num_lists}])
       (if (n.> 0 num_lists)
         (let [(open "[0]") ..functor
@@ -542,7 +542,7 @@
               list_vars (each product.right vars+lists)
               code (` (is (, zipped_type)
                           (function ((, g!step) (, g!func) (,* list_vars))
-                            (case [(,* list_vars)]
+                            (.when [(,* list_vars)]
                               (, pattern)
                               {.#Item ((, g!func) (,* (each product.left vars+lists)))
                                       ((, g!step) (, g!func) (,* list_vars))}
@@ -560,7 +560,7 @@
 
 (def .public (last xs)
   (All (_ a) (-> (List a) (Maybe a)))
-  (case xs
+  (.when xs
     {.#End}
     {.#None}
 
@@ -572,7 +572,7 @@
 
 (def .public (inits xs)
   (All (_ a) (-> (List a) (Maybe (List a))))
-  (case xs
+  (.when xs
     {.#End}
     {.#None}
 
@@ -580,7 +580,7 @@
     {.#Some {.#End}}
     
     {.#Item x xs'}
-    (case (inits xs')
+    (.when (inits xs')
       {.#None}
       (undefined)
 
@@ -620,7 +620,7 @@
   (All (_ a) (-> (List a) (List [Nat a])))
   (loop (again [idx 0
                 xs xs])
-    (case xs
+    (.when xs
       {.#End}
       {.#End}
 
@@ -629,7 +629,7 @@
 
 (def .public when
   (macro (_ tokens state)
-    (case tokens
+    (.when tokens
       (list test then)
       {.#Right [state (.list (` (.if (, test)
                                   (, then)
@@ -640,11 +640,11 @@
 
 (def .public (revised item revision it)
   (All (_ a) (-> Nat (-> a a) (List a) (List a)))
-  (case it
+  (.when it
     {.#End}
     {.#End}
 
     {.#Item head tail}
-    (case item
+    (.when item
       0 {.#Item (revision head) tail}
       _ (revised (-- item) revision it))))
diff --git a/stdlib/source/library/lux/data/collection/list/property.lux b/stdlib/source/library/lux/data/collection/list/property.lux
index a4480dabb..d249a3a4f 100644
--- a/stdlib/source/library/lux/data/collection/list/property.lux
+++ b/stdlib/source/library/lux/data/collection/list/property.lux
@@ -33,7 +33,7 @@
 
 (def .public (value key properties)
   (All (_ a) (-> Text (List a) (Maybe a)))
-  (case properties
+  (when properties
     {.#End}
     {.#None}
 
@@ -53,7 +53,7 @@
 
 (def .public (contains? key properties)
   (All (_ a) (-> Text (List a) Bit))
-  (case (..value key properties)
+  (when (..value key properties)
     {.#Some _}
     true
 
@@ -62,7 +62,7 @@
 
 (def .public (has key val properties)
   (All (_ a) (-> Text a (List a) (List a)))
-  (case properties
+  (when properties
     {.#End}
     (list [key val])
 
@@ -75,7 +75,7 @@
 
 (def .public (revised key f properties)
   (All (_ a) (-> Text (-> a a) (List a) (List a)))
-  (case properties
+  (when properties
     {.#End}
     {.#End}
 
@@ -86,7 +86,7 @@
 
 (def .public (lacks key properties)
   (All (_ a) (-> Text (List a) (List a)))
-  (case properties
+  (when properties
     {.#End}
     properties
 
diff --git a/stdlib/source/library/lux/data/collection/queue.lux b/stdlib/source/library/lux/data/collection/queue.lux
index 0420c1954..05a5107c3 100644
--- a/stdlib/source/library/lux/data/collection/queue.lux
+++ b/stdlib/source/library/lux/data/collection/queue.lux
@@ -53,7 +53,7 @@
 
 (def .public (next queue)
   (All (_ a) (-> (Queue a) (Queue a)))
-  (case (the #front queue)
+  (when (the #front queue)
     ... Empty...
     (.list)
     queue
@@ -71,7 +71,7 @@
 
 (def .public (end val queue)
   (All (_ a) (-> a (Queue a) (Queue a)))
-  (case (the #front queue)
+  (when (the #front queue)
     {.#End}
     (has #front (.list val) queue)
 
diff --git a/stdlib/source/library/lux/data/collection/queue/priority.lux b/stdlib/source/library/lux/data/collection/queue/priority.lux
index 0d02d0a09..bbd66f362 100644
--- a/stdlib/source/library/lux/data/collection/queue/priority.lux
+++ b/stdlib/source/library/lux/data/collection/queue/priority.lux
@@ -53,13 +53,13 @@
 
   (def .public (size queue)
     (All (_ a) (-> (Queue a) Nat))
-    (case (representation queue)
+    (when (representation queue)
       {.#None}
       0
 
       {.#Some tree}
       (loop (again [node tree])
-        (case (tree.root node)
+        (when (tree.root node)
           {0 #0 _}
           1
 
@@ -68,13 +68,13 @@
 
   (def .public (member? equivalence queue member)
     (All (_ a) (-> (Equivalence a) (Queue a) a Bit))
-    (case (representation queue)
+    (when (representation queue)
       {.#None}
       false
 
       {.#Some tree}
       (loop (again [node tree])
-        (case (tree.root node)
+        (when (tree.root node)
           {0 #0 reference}
           (at equivalence = reference member)
 
@@ -89,7 +89,7 @@
        [tree (representation queue)
         .let [highest_priority (tree.tag tree)]]
        (loop (again [node tree])
-         (case (tree.root node)
+         (when (tree.root node)
            {0 #0 reference}
            (if (n.= highest_priority (tree.tag node))
              {.#None}
@@ -97,13 +97,13 @@
 
            {0 #1 left right}
            (if (n.= highest_priority (tree.tag left))
-             (case (again left)
+             (when (again left)
                {.#None}
                {.#Some right}
 
                {.#Some =left}
                {.#Some (at ..builder branch =left right)})
-             (case (again right)
+             (when (again right)
                {.#None}
                {.#Some left}
 
@@ -114,7 +114,7 @@
     (All (_ a) (-> Priority a (Queue a) (Queue a)))
     (let [addition (at ..builder leaf priority value)]
       (abstraction
-       (case (representation queue)
+       (when (representation queue)
          {.#None}
          {.#Some addition}
 
diff --git a/stdlib/source/library/lux/data/collection/sequence.lux b/stdlib/source/library/lux/data/collection/sequence.lux
index 060c5a255..55c782acf 100644
--- a/stdlib/source/library/lux/data/collection/sequence.lux
+++ b/stdlib/source/library/lux/data/collection/sequence.lux
@@ -118,7 +118,7 @@
                    (if (array.lacks? sub_idx parent)
                      ... If so, set the path to the tail
                      (..path (level_down level) tail)
-                     (case (array.item sub_idx parent)
+                     (when (array.item sub_idx parent)
                        ... If not, push the tail onto the sub_node.
                        {#Hierarchy sub_node}
                        {#Hierarchy (with_tail size (level_down level) tail sub_node)}
@@ -138,7 +138,7 @@
 (def (hierarchy#has level idx val hierarchy)
   (All (_ a) (-> Level Index a (Hierarchy a) (Hierarchy a)))
   (let [sub_idx (branch_idx (i64.right_shifted level idx))]
-    (case (array.item sub_idx hierarchy)
+    (when (array.item sub_idx hierarchy)
       {#Hierarchy sub_node}
       (|> (array.clone hierarchy)
           (array.has! sub_idx {#Hierarchy (hierarchy#has (level_down level) idx val sub_node)}))
@@ -165,7 +165,7 @@
             (maybe#each (function (_ sub)
                           (|> (array.clone hierarchy)
                               (array.has! sub_idx {#Hierarchy sub})))
-                        (case (array.item sub_idx hierarchy)
+                        (when (array.item sub_idx hierarchy)
                           {#Hierarchy sub}
                           (without_tail size (level_down level) sub)
 
@@ -180,7 +180,7 @@
 
 (def (node#list node)
   (All (_ a) (-> (Node a) (List a)))
-  (case node
+  (when node
     {#Base base}
     (array.list {.#None} base)
     
@@ -264,7 +264,7 @@
         (let [index (branch_idx (i64.right_shifted level idx))]
           (if (array.lacks? index hierarchy)
             (exception.except ..base_was_not_found [])
-            (case [(n.> branching_exponent level)
+            (when [(n.> branching_exponent level)
                    (array.item index hierarchy)]
               [.true {#Hierarchy sub}]
               (again (level_down level) sub)
@@ -307,7 +307,7 @@
 
 (def .public (prefix sequence)
   (All (_ a) (-> (Sequence a) (Sequence a)))
-  (case (the #size sequence)
+  (when (the #size sequence)
     0
     empty
 
@@ -332,7 +332,7 @@
                                    (with_expansions [<else> [level root]]
                                      (if (n.> branching_exponent level)
                                        (if (array.lacks? 1 root)
-                                         (case (array.item 0 root)
+                                         (when (array.item 0 root)
                                            {#Hierarchy sub_node}
                                            (again (level_down level) sub_node)
 
@@ -375,7 +375,7 @@
   (All (_ a) (-> (Equivalence a) (Equivalence (Node a))))
   (implementation
    (def (= v1 v2)
-     (case [v1 v2]
+     (when [v1 v2]
        [{#Base b1} {#Base b2}]
        (array.= //#= b1 b2)
        
@@ -400,7 +400,7 @@
   (Mix Node)
   (implementation
    (def (mix $ init xs)
-     (case xs
+     (when xs
        {#Base base}
        (array.mix (function (_ _ item output) ($ item output))
                   init
@@ -434,7 +434,7 @@
   (Functor Node)
   (implementation
    (def (each $ xs)
-     (case xs
+     (when xs
        {#Base base}
        {#Base (array.each $ base)}
        
@@ -491,7 +491,7 @@
      (let [help (is (All (_ a)
                       (-> (Predicate a) (Node a) Bit))
                     (function (help predicate node)
-                      (case node
+                      (when node
                         {#Base base}
                         (<array> predicate base)
 
@@ -518,7 +518,7 @@
 (def (one|node check items)
   (All (_ a b)
     (-> (-> a (Maybe b)) (Node a) (Maybe b)))
-  (case items
+  (when items
     {#Base items}
     (array.one check items)
     
@@ -528,7 +528,7 @@
 (def .public (one check items)
   (All (_ a b)
     (-> (-> a (Maybe b)) (Sequence a) (Maybe b)))
-  (case (let [... TODO: This binding was established to get around a compilation error. Fix and inline!
+  (when (let [... TODO: This binding was established to get around a compilation error. Fix and inline!
               check (..one|node check)]
           (|> items
               (the #root)
diff --git a/stdlib/source/library/lux/data/collection/set/multi.lux b/stdlib/source/library/lux/data/collection/set/multi.lux
index 3b3e2039d..e08756a80 100644
--- a/stdlib/source/library/lux/data/collection/set/multi.lux
+++ b/stdlib/source/library/lux/data/collection/set/multi.lux
@@ -34,7 +34,7 @@
 
   (def .public (has multiplicity elem set)
     (All (_ a) (-> Nat a (Set a) (Set a)))
-    (case multiplicity
+    (when multiplicity
       0 set
       _ (|> set
             representation
@@ -43,9 +43,9 @@
 
   (def .public (lacks multiplicity elem set)
     (All (_ a) (-> Nat a (Set a) (Set a)))
-    (case multiplicity
+    (when multiplicity
       0 set
-      _ (case (dictionary.value elem (representation set))
+      _ (when (dictionary.value elem (representation set))
           {.#Some current}
           (abstraction
            (if (n.> multiplicity current)
diff --git a/stdlib/source/library/lux/data/collection/stack.lux b/stdlib/source/library/lux/data/collection/stack.lux
index c53ba235a..c037e1a56 100644
--- a/stdlib/source/library/lux/data/collection/stack.lux
+++ b/stdlib/source/library/lux/data/collection/stack.lux
@@ -28,7 +28,7 @@
 
   (def .public (value stack)
     (All (_ a) (-> (Stack a) (Maybe a)))
-    (case (representation stack)
+    (when (representation stack)
       {.#End}
       {.#None}
       
@@ -37,7 +37,7 @@
 
   (def .public (next stack)
     (All (_ a) (-> (Stack a) (Maybe [a (Stack a)])))
-    (case (representation stack)
+    (when (representation stack)
       {.#End}
       {.#None}
       
diff --git a/stdlib/source/library/lux/data/collection/stream.lux b/stdlib/source/library/lux/data/collection/stream.lux
index 3c3a2cb29..bf39422ee 100644
--- a/stdlib/source/library/lux/data/collection/stream.lux
+++ b/stdlib/source/library/lux/data/collection/stream.lux
@@ -39,7 +39,7 @@
     (-> [a (List a)] (Stream a)))
   (loop (again [head start
                 tail next])
-    (//.pending [head (case tail
+    (//.pending [head (when tail
                         {.#End}
                         (again start next)
                         
@@ -59,7 +59,7 @@
 (def .public (item idx stream)
   (All (_ a) (-> Nat (Stream a) a))
   (let [[head tail] (//.result stream)]
-    (case idx
+    (when idx
       0 head
       _ (item (-- idx) tail))))
 
diff --git a/stdlib/source/library/lux/data/collection/tree/finger.lux b/stdlib/source/library/lux/data/collection/tree/finger.lux
index b8a654516..68d7e7157 100644
--- a/stdlib/source/library/lux/data/collection/tree/finger.lux
+++ b/stdlib/source/library/lux/data/collection/tree/finger.lux
@@ -58,7 +58,7 @@
 
   (def .public (value tree)
     (All (_ @ t v) (-> (Tree @ t v) v))
-    (case (the #root (representation tree))
+    (when (the #root (representation tree))
       {0 #0 value}
       value
 
@@ -67,7 +67,7 @@
 
   (def .public (tags tree)
     (All (_ @ t v) (-> (Tree @ t v) (List t)))
-    (case (the #root (representation tree))
+    (when (the #root (representation tree))
       {0 #0 value}
       (list (the #tag (representation tree)))
 
@@ -77,7 +77,7 @@
 
   (def .public (values tree)
     (All (_ @ t v) (-> (Tree @ t v) (List v)))
-    (case (the #root (representation tree))
+    (when (the #root (representation tree))
       {0 #0 value}
       (list value)
 
@@ -92,7 +92,7 @@
         (let [(open "tag//[0]") monoid]
           (loop (again [_tag tag//identity
                         _node root])
-            (case _node
+            (when _node
               {0 #0 value}
               {.#Some value}
 
@@ -106,7 +106,7 @@
 
 (def .public (exists? predicate tree)
   (All (_ @ t v) (-> (Predicate t) (Tree @ t v) Bit))
-  (case (..one predicate tree)
+  (when (..one predicate tree)
     {.#Some _}
     true
 
diff --git a/stdlib/source/library/lux/data/collection/tree/zipper.lux b/stdlib/source/library/lux/data/collection/tree/zipper.lux
index 1e403280e..b06a5c591 100644
--- a/stdlib/source/library/lux/data/collection/tree/zipper.lux
+++ b/stdlib/source/library/lux/data/collection/tree/zipper.lux
@@ -80,7 +80,7 @@
 
 (def .public (start? zipper)
   (All (_ a) (-> (Zipper a) Bit))
-  (case (the #family zipper)
+  (when (the #family zipper)
     {.#None}
     true
 
@@ -89,7 +89,7 @@
 
 (def .public (down zipper)
   (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-  (case (..children zipper)
+  (when (..children zipper)
     {.#End}
     {.#None}
 
@@ -120,9 +120,9 @@
 (with_template [<one> <all> <side> <op_side>]
   [(def .public (<one> zipper)
      (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-     (case (the #family zipper)
+     (when (the #family zipper)
        {.#Some family}
-       (case (the <side> family)
+       (when (the <side> family)
          {.#Item next side'}
          {.#Some (for @.old
                       [#family {.#Some (|> family
@@ -144,12 +144,12 @@
 
    (def .public (<all> zipper)
      (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-     (case (the #family zipper)
+     (when (the #family zipper)
        {.#None}
        {.#None}
 
        {.#Some family}
-       (case (list.reversed (the <side> family))
+       (when (list.reversed (the <side> family))
          {.#End}
          {.#None}
 
@@ -173,13 +173,13 @@
 
 (def .public (next zipper)
   (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-  (case (..down zipper)
+  (when (..down zipper)
     {.#Some forward}
     {.#Some forward}
     
     {.#None}
     (loop (again [@ zipper])
-      (case (..right @)
+      (when (..right @)
         {.#Some forward}
         {.#Some forward}
         
@@ -190,12 +190,12 @@
 
 (def (bottom zipper)
   (All (_ a) (-> (Zipper a) (Zipper a)))
-  (case (..right zipper)
+  (when (..right zipper)
     {.#Some forward}
     (bottom forward)
 
     {.#None}
-    (case (..down zipper)
+    (when (..down zipper)
       {.#Some forward}
       (bottom forward)
 
@@ -204,12 +204,12 @@
 
 (def .public (previous zipper)
   (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-  (case (..left zipper)
+  (when (..left zipper)
     {.#None}
     (..up zipper)
 
     {.#Some backward}
-    {.#Some (case (..down backward)
+    {.#Some (when (..down backward)
               {.#Some then}
               (..bottom then)
 
@@ -219,13 +219,13 @@
 (with_template [<name> <move>]
   [(def .public (<name> zipper)
      (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
-     (case (<move> zipper)
+     (when (<move> zipper)
        {.#None}
        {.#None}
 
        {.#Some @}
        (loop (again [@ @])
-         (case (<move> @)
+         (when (<move> @)
            {.#None}
            {.#Some @}
 
@@ -238,7 +238,7 @@
 
 (def .public (end? zipper)
   (All (_ a) (-> (Zipper a) Bit))
-  (case (..end zipper)
+  (when (..end zipper)
     {.#None}
     true
 
@@ -261,7 +261,7 @@
   (All (_ a) (-> (Zipper a) (Maybe (Zipper a))))
   (do maybe.monad
     [family (the #family zipper)]
-    (case (the #lefts family)
+    (when (the #lefts family)
       {.#End}
       (in (has [#node //.#children]
                (the #rights family)
@@ -277,7 +277,7 @@
 (with_template [<name> <side>]
   [(def .public (<name> value zipper)
      (All (_ a) (-> a (Zipper a) (Maybe (Zipper a))))
-     (case (the #family zipper)
+     (when (the #family zipper)
        {.#None}
        {.#None}
 
diff --git a/stdlib/source/library/lux/data/color.lux b/stdlib/source/library/lux/data/color.lux
index bbccf6b7b..61e3d5593 100644
--- a/stdlib/source/library/lux/data/color.lux
+++ b/stdlib/source/library/lux/data/color.lux
@@ -249,9 +249,9 @@
         t (|> +1.0 (f.- (|> +1.0 (f.- f) (f.* saturation))) (f.* brightness))
         v brightness
         mod (|> i (f.% +6.0) f.int .nat)
-        red (case mod 0 v 1 q 2 p 3 p 4 t 5 v _ (undefined))
-        green (case mod 0 t 1 v 2 v 3 q 4 p 5 p _ (undefined))
-        blue (case mod 0 p 1 p 2 t 3 v 4 v 5 q _ (undefined))]
+        red (when mod 0 v 1 q 2 p 3 p 4 t 5 v _ (undefined))
+        green (when mod 0 t 1 v 2 v 3 q 4 p 5 p _ (undefined))
+        blue (when mod 0 p 1 p 2 t 3 v 4 v 5 q _ (undefined))]
     (of_rgb [#red (..up red)
              #green (..up green)
              #blue (..up blue)])))
diff --git a/stdlib/source/library/lux/data/format/css.lux b/stdlib/source/library/lux/data/format/css.lux
index 80b0623cd..600068d16 100644
--- a/stdlib/source/library/lux/data/format/css.lux
+++ b/stdlib/source/library/lux/data/format/css.lux
@@ -55,7 +55,7 @@
 
   (def .public (font font)
     (-> Font (CSS Special))
-    (let [with_unicode (case (the /font.#unicode_range font)
+    (let [with_unicode (when (the /font.#unicode_range font)
                          {.#Some unicode_range}
                          (let [unicode_range' (format "U+" (at nat.hex encoded (the /font.#start unicode_range))
                                                       "-" (at nat.hex encoded (the /font.#end unicode_range)))]
@@ -79,7 +79,7 @@
   (def .public (import url query)
     (-> URL (Maybe Query) (CSS Special))
     (abstraction (format (format "@import url(" (%.text url) ")")
-                         (case query
+                         (when query
                            {.#Some query}
                            (format " " (/query.query query))
                            
diff --git a/stdlib/source/library/lux/data/format/css/value.lux b/stdlib/source/library/lux/data/format/css/value.lux
index 3845d2cb6..4675c0385 100644
--- a/stdlib/source/library/lux/data/format/css/value.lux
+++ b/stdlib/source/library/lux/data/format/css/value.lux
@@ -918,7 +918,7 @@
 
       (def (with_hint [hint stop])
         (-> [(Maybe Hint) Stop] Text)
-        (case hint
+        (when hint
           {.#None}
           (representation Stop stop)
           
@@ -1073,7 +1073,7 @@
            Stop (List/1 [(Maybe Hint) Stop])
            (Value Image))
        (let [after_extent (format "at " (representation location))
-             with_extent (case extent
+             with_extent (when extent
                            {.#Some extent}
                            (format (..extent extent) " " after_extent)
                            
@@ -1155,7 +1155,7 @@
 
     (def .public (font_family options)
       (-> (List Font) (Value Font))
-      (case options
+      (when options
         {.#Item _}
         (|> options
             (list#each ..font_name)
diff --git a/stdlib/source/library/lux/data/format/html.lux b/stdlib/source/library/lux/data/format/html.lux
index 15d20bb2d..d01f92b22 100644
--- a/stdlib/source/library/lux/data/format/html.lux
+++ b/stdlib/source/library/lux/data/format/html.lux
@@ -46,7 +46,7 @@
 
 (def (target value)
   (-> Target Text)
-  (case value
+  (when value
     {#Blank} "_blank"
     {#Parent} "_parent"
     {#Self} "_self"
@@ -176,7 +176,7 @@
   (def .public (base href target)
     (-> URL (Maybe Target) Meta)
     (let [partial (list ["href" href])
-          full (case target
+          full (when target
                  {.#Some target}
                  (list.partial ["target" (..target target)] partial)
                  
@@ -286,7 +286,7 @@
   
   (def (area attributes shape)
     (-> Attributes Shape (HTML Any))
-    (case shape
+    (when shape
       {#Rectangle rectangle}
       (..rectangle attributes rectangle)
       
@@ -300,7 +300,7 @@
     (-> Attributes (List [Attributes Shape]) Image Image)
     (all ..and
          for
-         (case (list#each (product.uncurried ..area) areas)
+         (when (list#each (product.uncurried ..area) areas)
            {.#End}
            (..empty "map" attributes)
            
@@ -348,7 +348,7 @@
     [(def .public (<name> description attributes content)
        (-> (Maybe Content) Attributes <type> <type>)
        (..tag <container_tag> attributes
-              (case description
+              (when description
                 {.#Some description}
                 (all ..and
                      (..tag <description_tag> (list) description)
@@ -462,7 +462,7 @@
 
   (def .public (description_list attributes descriptions)
     (-> Attributes (List [Content Element]) Element)
-    (case (list#each (function (_ [term description])
+    (when (list#each (function (_ [term description])
                        (all ..and
                             (..term term)
                             (..description description)))
@@ -524,7 +524,7 @@
   (def .public (table attributes caption columns headers rows footer)
     (-> Attributes (Maybe Content) (Maybe Column) Header (List Cell) (Maybe Cell) Element)
     (let [head (..table_head (..table_row headers))
-          content (case (list#each table_row rows)
+          content (when (list#each table_row rows)
                     {.#End}
                     head
 
@@ -532,21 +532,21 @@
                     (..and head
                            (..table_body
                             (list#mix (function.flipped ..and) first rest))))
-          content (case footer
+          content (when footer
                     {.#None}
                     content
                     
                     {.#Some footer}
                     (..and content
                            (..table_foot (..table_row footer))))
-          content (case columns
+          content (when columns
                     {.#None}
                     content
                     
                     {.#Some columns}
                     (..and (..columns_group columns)
                            content))
-          content (case caption
+          content (when caption
                     {.#None}
                     content
 
diff --git a/stdlib/source/library/lux/data/format/json.lux b/stdlib/source/library/lux/data/format/json.lux
index 3dd15f400..a5b036478 100644
--- a/stdlib/source/library/lux/data/format/json.lux
+++ b/stdlib/source/library/lux/data/format/json.lux
@@ -62,7 +62,7 @@
 
 (def .public null?
   (Predicate JSON)
-  (|>> (pipe.case {#Null} true
+  (|>> (pipe.when {#Null} true
          _ false)))
 
 (def .public object
@@ -98,7 +98,7 @@
 
 (def (jsonF token)
   (-> JSON' Code)
-  (case token
+  (when token
     {#Null' _}
     (` {..#Null})
     
@@ -128,7 +128,7 @@
 
 (def .public (fields json)
   (-> JSON (Try (List String)))
-  (case json
+  (when json
     {#Object obj}
     {try.#Success (dictionary.keys obj)}
 
@@ -137,9 +137,9 @@
 
 (def .public (field key json)
   (-> String JSON (Try JSON))
-  (case json
+  (when json
     {#Object obj}
-    (case (dictionary.value key obj)
+    (when (dictionary.value key obj)
       {.#Some value}
       {try.#Success value}
 
@@ -151,7 +151,7 @@
 
 (def .public (has key value json)
   (-> String JSON JSON (Try JSON))
-  (case json
+  (when json
     {#Object obj}
     {try.#Success {#Object (dictionary.has key value obj)}}
 
@@ -161,7 +161,7 @@
 (with_template [<name> <tag> <type>]
   [(def .public (<name> key json)
      (-> Text JSON (Try <type>))
-     (case (field key json)
+     (when (field key json)
        {try.#Success {<tag> value}}
        {try.#Success value}
 
@@ -182,7 +182,7 @@
   (Equivalence JSON)
   (implementation
    (def (= x y)
-     (case [x y]
+     (when [x y]
        [{#Null} {#Null}]
        true
 
@@ -209,7 +209,7 @@
        (and (n.= (dictionary.size xs) (dictionary.size ys))
             (list#mix (function (_ [xk xv] prev)
                         (and prev
-                             (case (dictionary.value xk ys)
+                             (when (dictionary.value xk ys)
                                {.#None}    false
                                {.#Some yv} (= xv yv))))
                       true
@@ -228,7 +228,7 @@
 
 (def boolean_format
   (-> Boolean Text)
-  (|>> (pipe.case
+  (|>> (pipe.when
          .false
          "false"
          
@@ -237,7 +237,7 @@
 
 (def number_format
   (-> Number Text)
-  (|>> (pipe.case
+  (|>> (pipe.when
          +0.0 ... OR -0.0
          "0.0"
 
@@ -294,7 +294,7 @@
 
 (def .public (format json)
   (-> JSON Text)
-  (case json
+  (when json
     (^.with_template [<tag> <format>]
       [{<tag> value}
        (<format> value)])
@@ -359,7 +359,7 @@
                      signed?' (<>.parses? (<text>.this "-"))
                      offset (<text>.many <text>.decimal)]
                     (in (all text#composite mark (if signed?' "-" "") offset))))]
-    (case (f#decoded (all text#composite (if signed? "-" "") digits "." decimals exp))
+    (when (f#decoded (all text#composite (if signed? "-" "") digits "." decimals exp))
       {try.#Failure message}
       (<>.failure message)
       
diff --git a/stdlib/source/library/lux/data/format/markdown.lux b/stdlib/source/library/lux/data/format/markdown.lux
index 4b8e1a4a2..f6faa4820 100644
--- a/stdlib/source/library/lux/data/format/markdown.lux
+++ b/stdlib/source/library/lux/data/format/markdown.lux
@@ -110,7 +110,7 @@
     (|>> list.enumeration
          (list#each (function (_ [idx [summary detail]])
                       (format "1. " (representation summary)
-                              (case detail
+                              (when detail
                                 {.#Some detail}
                                 (|> detail
                                     representation
@@ -128,7 +128,7 @@
         (Markdown Block))
     (|>> (list#each (function (_ [summary detail])
                       (format "* " (representation summary)
-                              (case detail
+                              (when detail
                                 {.#Some detail}
                                 (|> detail
                                     representation
diff --git a/stdlib/source/library/lux/data/format/tar.lux b/stdlib/source/library/lux/data/format/tar.lux
index aad8579af..360ceeb11 100644
--- a/stdlib/source/library/lux/data/format/tar.lux
+++ b/stdlib/source/library/lux/data/format/tar.lux
@@ -236,16 +236,16 @@
 
 (def (un_padded string)
   (-> Binary Binary)
-  (case (binary!.size string)
+  (when (binary!.size string)
     0
     string
     
     size
     (loop (again [end (-- size)])
-      (case end
+      (when end
         0 (at utf8.codec encoded "")
         _ (let [last_char (binary!.bits_8 end string)]
-            (`` (case (.nat last_char)
+            (`` (when (.nat last_char)
                   (char (,, (static ..null)))
                   (again (-- end))
 
@@ -434,7 +434,7 @@
       (Parser Link_Flag)
       (do <>.monad
         [it <binary>.bits_8]
-        (case (.nat it)
+        (when (.nat it)
           (^.with_template [<value> <link_flag>]
             [<value>
              (in <link_flag>)])
@@ -597,7 +597,7 @@
   (-> Big Nat)
   (n.+ (n./ ..block_size
             (..from_big size))
-       (case (n.% ..block_size (..from_big size))
+       (when (n.% ..block_size (..from_big size))
          0 0
          _ 1)))
 
@@ -729,7 +729,7 @@
 
 (def entry_format
   (Format Entry)
-  (|>> (pipe.case
+  (|>> (pipe.when
          {#Normal value} (..normal_file_format value)
          {#Symbolic_Link value} (..symbolic_link_format value)
          {#Directory value} (..directory_format value)
diff --git a/stdlib/source/library/lux/data/format/xml.lux b/stdlib/source/library/lux/data/format/xml.lux
index 3635c56f3..0978967f1 100644
--- a/stdlib/source/library/lux/data/format/xml.lux
+++ b/stdlib/source/library/lux/data/format/xml.lux
@@ -62,7 +62,7 @@
             (<>.codec int.decimal)
             <text>.slice
             <text>.many!
-            (case hex?
+            (when hex?
               {.#None}
               <text>.decimal!
 
@@ -95,7 +95,7 @@
   (do <>.monad
     [first_part xml_identifier
      ?second_part (<| <>.maybe (<>.after (<text>.this ..namespace_separator)) xml_identifier)]
-    (case ?second_part
+    (when ?second_part
       {.#None}
       (in ["" first_part])
 
@@ -213,7 +213,7 @@
 
 (def .public (tag [namespace name])
   (-> Tag Text)
-  (case namespace
+  (when namespace
     "" name
     _ (all text#composite namespace ..namespace_separator name)))
 
@@ -248,7 +248,7 @@
               ..xml_header text.new_line
               (loop (again [prefix ""
                             input input])
-                (case input
+                (when input
                   {#Text value}
                   (sanitize_value value)
 
@@ -282,7 +282,7 @@
   (Equivalence XML)
   (implementation
    (def (= reference sample)
-     (case [reference sample]
+     (when [reference sample]
        [{#Text reference/value} {#Text sample/value}]
        (text#= reference/value sample/value)
 
diff --git a/stdlib/source/library/lux/data/sum.lux b/stdlib/source/library/lux/data/sum.lux
index 03e26b25d..0ed2931d1 100644
--- a/stdlib/source/library/lux/data/sum.lux
+++ b/stdlib/source/library/lux/data/sum.lux
@@ -19,7 +19,7 @@
     (-> (-> a c) (-> b c)
         (-> (Or a b) c)))
   (function (_ input)
-    (case input
+    (when input
       {0 #0 l} (on_left l)
       {0 #1 r} (on_right r))))
 
@@ -28,14 +28,14 @@
     (-> (-> l l') (-> r r')
         (-> (Or l r) (Or l' r'))))
   (function (_ input)
-    (case input
+    (when input
       {0 #0 l} {0 #0 (on_left l)}
       {0 #1 r} {0 #1 (on_right r)})))
 
 (with_template [<name> <side> <right?>]
   [(def .public (<name> items)
      (All (_ a b) (-> (List (Or a b)) (List <side>)))
-     (case items
+     (when items
        {.#End}
        {.#End}
        
@@ -51,13 +51,13 @@
 
 (def .public (partition xs)
   (All (_ a b) (-> (List (Or a b)) [(List a) (List b)]))
-  (case xs
+  (when xs
     {.#End}
     [{.#End} {.#End}]
 
     {.#Item x xs'}
     (let [[lefts rights] (partition xs')]
-      (case x
+      (when x
         {0 #0 x'}  [{.#Item x' lefts} rights]
         {0 #1 x'} [lefts {.#Item x' rights}]))))
 
@@ -65,7 +65,7 @@
   (All (_ l r) (-> (Equivalence l) (Equivalence r) (Equivalence (Or l r))))
   (implementation
    (def (= reference sample)
-     (case [reference sample]
+     (when [reference sample]
        [{.#Left reference} {.#Left sample}]
        (at left = reference sample)
 
@@ -82,7 +82,7 @@
      (..equivalence (at left equivalence)
                     (at right equivalence)))
    (def (hash value)
-     (.nat (case value
+     (.nat (when value
              {.#Left value}
              ("lux i64 *" +2 (.int (at left hash value)))
 
diff --git a/stdlib/source/library/lux/data/text.lux b/stdlib/source/library/lux/data/text.lux
index e9fa52957..8502d1d76 100644
--- a/stdlib/source/library/lux/data/text.lux
+++ b/stdlib/source/library/lux/data/text.lux
@@ -71,7 +71,7 @@
                 output (is (Maybe Nat)
                            {.#None})])
     (let [output' ("lux text index" offset part text)]
-      (case output'
+      (when output'
         {.#None}
         output
 
@@ -80,7 +80,7 @@
 
 (def .public (starts_with? prefix x)
   (-> Text Text Bit)
-  (case (index prefix x)
+  (when (index prefix x)
     {.#Some 0}
     true
 
@@ -89,7 +89,7 @@
 
 (def .public (ends_with? postfix x)
   (-> Text Text Bit)
-  (case (last_index postfix x)
+  (when (last_index postfix x)
     {.#Some n}
     (n.= (size x)
          (n.+ (size postfix) n))
@@ -104,7 +104,7 @@
 
 (def .public (contains? sub text)
   (-> Text Text Bit)
-  (case ("lux text index" 0 sub text)
+  (when ("lux text index" 0 sub text)
     {.#Some _}
     true
 
@@ -146,7 +146,7 @@
 
 (def .public (split_at at x)
   (-> Nat Text (Maybe [Text Text]))
-  (case [(..clip 0 at x) (..clip_since at x)]
+  (when [(..clip 0 at x) (..clip_since at x)]
     [{.#Some pre} {.#Some post}]
     {.#Some [pre post]}
 
@@ -165,7 +165,7 @@
   (-> Text Text (List Text))
   (loop (again [input sample
                 output (is (List Text) (list))])
-    (case (..split_by token input)
+    (when (..split_by token input)
       {.#Some [pre post]}
       (|> output
           {.#Item pre}
@@ -185,9 +185,9 @@
 
 (for @.js (these (def defined?
                    (macro (_ tokens lux)
-                     (case tokens
+                     (when tokens
                        (list it)
-                       {.#Right [lux (list (` (.case ("js type-of" ("js constant" (, it)))
+                       {.#Right [lux (list (` (.when ("js type-of" ("js constant" (, it)))
                                                 "undefined"
                                                 .false
 
@@ -198,7 +198,7 @@
                        {.#Left ""})))
                  (def if_nashorn
                    (macro (_ tokens lux)
-                     (case tokens
+                     (when tokens
                        (list then else)
                        {.#Right [lux (list (if (and (..defined? "java")
                                                     (..defined? "java.lang")
@@ -215,7 +215,7 @@
   (with_expansions [... Inefficient default
                     <default> (loop (again [left ""
                                             right template])
-                                (case (..split_by pattern right)
+                                (when (..split_by pattern right)
                                   {.#Some [pre post]}
                                   (again (all "lux text concat" left pre replacement) post)
 
@@ -320,13 +320,13 @@
 
 (def .public (interposed separator texts)
   (-> Text (List Text) Text)
-  (case separator
+  (when separator
     "" (..together texts)
     _ (|> texts (list.interposed separator) ..together)))
 
 (def .public (empty? text)
   (-> Text Bit)
-  (case text
+  (when text
     "" true
     _  false))
 
@@ -347,7 +347,7 @@
                                 [..carriage_return]
                                 [..form_feed]
                                 )]
-    (`` (case char
+    (`` (when char
           <options>
 
           _
diff --git a/stdlib/source/library/lux/data/text/escape.lux b/stdlib/source/library/lux/data/text/escape.lux
index 85f038d05..2ce6021a6 100644
--- a/stdlib/source/library/lux/data/text/escape.lux
+++ b/stdlib/source/library/lux/data/text/escape.lux
@@ -72,7 +72,7 @@
   (-> Char Bit)
   (or (n.< ..ascii_bottom char)
       (n.> ..ascii_top char)
-      (case char
+      (when char
         (^.with_template [<char>]
           [<char>
            true])
@@ -97,7 +97,7 @@
   (-> Char Nat Nat Text Text [Text Text Nat])
   (let [code (at n.hex encoded char)
         replacement (format ..sigil "u"
-                            (case ("lux text size" code)
+                            (when ("lux text size" code)
                               1 (format "000" code)
                               2 (format "00" code)
                               3 (format "0" code)
@@ -117,7 +117,7 @@
                 current text
                 limit ("lux text size" text)])
     (if (n.< limit offset)
-      (case ("lux text char" offset current)
+      (when ("lux text char" offset current)
         (^.with_template [<char> <replacement>]
           [<char>
            (let [[previous' current' limit'] (ascii_escaped <replacement> offset limit previous current)]
@@ -180,7 +180,7 @@
 
 (def (unicode_un_escaped offset previous current limit)
   (-> Nat Text Text Nat (Try [Text Text Nat]))
-  (case (|> current
+  (when (|> current
             ("lux text clip" (n.+ ..ascii_escape_offset offset) ..code_size)
             (at n.hex decoded))
     {try.#Success char}
@@ -201,11 +201,11 @@
                 current text
                 limit ("lux text size" text)])
     (if (n.< limit offset)
-      (case ("lux text char" offset current)
+      (when ("lux text char" offset current)
         ..sigil_char
         (let [@sigil (++ offset)]
           (if (n.< limit @sigil)
-            (case ("lux text char" @sigil current)
+            (when ("lux text char" @sigil current)
               (^.with_template [<sigil> <un_escaped>]
                 [<sigil>
                  (let [[previous' current' limit'] (..ascii_un_escaped <un_escaped> offset previous current limit)]
@@ -235,13 +235,13 @@
 
         _
         (again (++ offset) previous current limit))
-      {try.#Success (case previous
+      {try.#Success (when previous
                       "" current
                       _ (format previous current))})))
 
 (def .public literal
   (syntax (_ [literal <code>.text])
-    (case (..un_escaped literal)
+    (when (..un_escaped literal)
       {try.#Success un_escaped}
       (in (list (code.text un_escaped)))
       
diff --git a/stdlib/source/library/lux/data/text/regex.lux b/stdlib/source/library/lux/data/text/regex.lux
index d8d094f6e..09dba9073 100644
--- a/stdlib/source/library/lux/data/text/regex.lux
+++ b/stdlib/source/library/lux/data/text/regex.lux
@@ -111,7 +111,7 @@
      parts (<>.many (all <>.either
                          re_range^
                          re_options^))]
-    (in (case negate?
+    (in (when negate?
           {.#Some _} (` (<text>.not (all <>.either (,* parts))))
           {.#None}   (` (all <>.either (,* parts)))))))
 
@@ -219,7 +219,7 @@
   (do <>.monad
     [base (re_simple^ current_module)
      quantifier (<text>.one_of "?*+")]
-    (case quantifier
+    (when quantifier
       "?"
       (in (` (<>.else "" (, base))))
       
@@ -290,7 +290,7 @@
                                              [Nat (List Code) (List (List Code))]
                                              [Nat (List Code) (List (List Code))])
                                          (function (_ part [idx names steps])
-                                           (case part
+                                           (when part
                                              (^.or {.#Left complex}
                                                    {.#Right [{#Non_Capturing} complex]})
                                              [idx
@@ -300,7 +300,7 @@
                                                             steps)]
                                              
                                              {.#Right [{#Capturing [?name num_captures]} scoped]}
-                                             (let [[idx! name!] (case ?name
+                                             (let [[idx! name!] (when ?name
                                                                   {.#Some _name}
                                                                   [idx (code.symbol ["" _name])]
 
@@ -335,12 +335,12 @@
 (def .public (or left right)
   (All (_ l r) (-> (Parser [Text l]) (Parser [Text r]) (Parser [Text (Or l r)])))
   (function (_ input)
-    (case (left input)
+    (when (left input)
       {try.#Success [input' [lt lv]]}
       {try.#Success [input' [lt {0 #0 lv}]]}
 
       {try.#Failure _}
-      (case (right input)
+      (when (right input)
         {try.#Success [input' [rt rv]]}
         {try.#Success [input' [rt {0 #1 rv}]]}
 
@@ -350,12 +350,12 @@
 (def .public (either left right)
   (All (_ l r) (-> (Parser [Text l]) (Parser [Text r]) (Parser Text)))
   (function (_ input)
-    (case (left input)
+    (when (left input)
       {try.#Success [input' [lt lv]]}
       {try.#Success [input' lt]}
 
       {try.#Failure _}
-      (case (right input)
+      (when (right input)
         {try.#Success [input' [rt rv]]}
         {try.#Success [input' rt]}
 
@@ -418,7 +418,7 @@
   (syntax (_ [pattern <code>.text])
     (do meta.monad
       [current_module meta.current_module_name]
-      (case (<text>.result (regex^ current_module)
+      (when (<text>.result (regex^ current_module)
                            pattern)
         {try.#Failure error}
         (meta.failure (format "Error while parsing regular-expression:" //.new_line
diff --git a/stdlib/source/library/lux/data/text/unicode/set.lux b/stdlib/source/library/lux/data/text/unicode/set.lux
index 13c5d4f47..771fb287f 100644
--- a/stdlib/source/library/lux/data/text/unicode/set.lux
+++ b/stdlib/source/library/lux/data/text/unicode/set.lux
@@ -217,7 +217,7 @@
     (-> Set Char Bit)
     (loop (again [tree (representation set)])
       (if (//block.within? (tree.tag tree) character)
-        (case (tree.root tree)
+        (when (tree.root tree)
           {0 #0 _}
           true