- Added exhaustiveness testing for exception-handling code.

- Added some optimizations for using List & Maybe within the compiler.

12 files changed, 186 insertions, 109 deletions

diff --git a/src/lux/analyser.clj b/src/lux/analyser.clj
index e1c167ce6..03709b226 100644
--- a/src/lux/analyser.clj
+++ b/src/lux/analyser.clj
@@ -364,7 +364,7 @@
     (&/$FormS (&/$Cons [_ (&/$SymbolS _ "_jvm_try")]
                        (&/$Cons ?body
                                 ?handlers)))
-    (|do [catches+finally (&/fold% parse-handler (&/T (&/|list) (&/V &/$None nil)) ?handlers)]
+    (|do [catches+finally (&/fold% parse-handler (&/T &/Nil$ &/None$) ?handlers)]
       (&&host/analyse-jvm-try analyse exo-type ?body catches+finally))
 
     (&/$FormS (&/$Cons [_ (&/$SymbolS _ "_jvm_throw")]
@@ -602,7 +602,7 @@
     (&&lux/analyse-record analyse exo-type ?elems)
 
     (&/$TagS ?ident)
-    (analyse-variant+ analyse exo-type ?ident (&/|list))
+    (analyse-variant+ analyse exo-type ?ident &/Nil$)
     
     (&/$SymbolS _ "_jvm_null")
     (&&host/analyse-jvm-null analyse exo-type)
diff --git a/src/lux/analyser/case.clj b/src/lux/analyser/case.clj
index a0f07cdce..109ba7c41 100644
--- a/src/lux/analyser/case.clj
+++ b/src/lux/analyser/case.clj
@@ -39,7 +39,7 @@
 
 ;; [Utils]
 (def ^:private unit
-  (&/T (&/T "" -1 -1) (&/V &/$TupleS (&/|list))))
+  (&/T (&/T "" -1 -1) (&/V &/$TupleS &/Nil$)))
 
 (defn ^:private resolve-type [type]
   (|case type
@@ -118,7 +118,7 @@
 
 (defn adjust-type [type]
   "(-> Type (Lux Type))"
-  (adjust-type* (&/|list) type))
+  (adjust-type* &/Nil$ type))
 
 (defn ^:private analyse-pattern [value-type pattern kont]
   (|let [[meta pattern*] pattern]
@@ -170,7 +170,7 @@
                                                      (|do [[=test [=tests =kont]] (analyse-pattern v m kont*)]
                                                        (return (&/T (&/Cons$ =test =tests) =kont)))))
                                                  (|do [=kont kont]
-                                                   (return (&/T (&/|list) =kont)))
+                                                   (return (&/T &/Nil$ =kont)))
                                                  (&/|reverse (&/zip2 ?member-types ?members)))]
                       (return (&/T (&/V $TupleTestAC =tests) =kont)))))
 
@@ -392,7 +392,7 @@
   (|do [patterns (&/fold% (fn [patterns branch]
                             (|let [[pattern body] branch]
                               (analyse-branch analyse exo-type value-type pattern body patterns)))
-                          (&/|list)
+                          &/Nil$
                           branches)
         struct (&/fold% merge-total (&/V $DefaultTotal false) patterns)
         ? (check-totality value-type struct)]
diff --git a/src/lux/analyser/host.clj b/src/lux/analyser/host.clj
index 0eb89b251..db04a60c0 100644
--- a/src/lux/analyser/host.clj
+++ b/src/lux/analyser/host.clj
@@ -23,6 +23,48 @@
     _
     (fail "[Analyser/Host Error] Can't extract text.")))
 
+(defn ^:private ensure-catching [exceptions]
+  "(-> (List Text) (Lux (,)))"
+  (|do [class-loader &/loader]
+    (fn [state]
+      (let [exceptions (&/|map #(Class/forName % true class-loader) exceptions)
+            catching (->> state (&/get$ &/$host) (&/get$ &/$catching)
+                          (&/|map #(Class/forName % true class-loader)))]
+        (if-let [missing-ex (&/fold (fn [prev now]
+                                      (or prev
+                                          (if (&/fold (fn [found? ex-catch]
+                                                        (or found?
+                                                            (.isAssignableFrom ex-catch now)))
+                                                      false
+                                                      catching)
+                                            nil
+                                            now)))
+                                    nil
+                                    exceptions)]
+          (assert false (str "[Analyser Error] Unhandled exception: " missing-ex))
+          ;; (&/fail* (str "[Analyser Error] Unhandled exception: " missing-ex))
+          (&/return* state nil)))
+      )))
+
+(defn ^:private with-catches [catches body]
+  "(All [a] (-> (List Text) (Lux a) (Lux a)))"
+  (fn [state]
+    (let [;; _ (prn 'with-catches/_0 (&/->seq catches))
+          old-catches (->> state (&/get$ &/$host) (&/get$ &/$catching))
+          ;; _ (prn 'with-catches/_1 (&/->seq (->> state (&/get$ &/$host) (&/get$ &/$catching))))
+          state* (->> state (&/update$ &/$host #(&/update$ &/$catching (partial &/|++ catches) %)))
+          ;; _ (prn 'with-catches/_2 (&/->seq (->> state* (&/get$ &/$host) (&/get$ &/$catching))))
+          ]
+      (|case (&/run-state body state*)
+        (&/$Left msg)
+        (&/V &/$Left msg)
+
+        (&/$Right state** output)
+        (do ;; (prn 'with-catches/_3 (&/->seq (->> state** (&/get$ &/$host) (&/get$ &/$catching))))
+            (&/V &/$Right (&/T (->> state** (&/update$ &/$host #(&/set$ &/$catching old-catches %)))
+                               output)))))
+    ))
+
 (defn ^:private analyse-1+ [analyse token]
   (&type/with-var
     (fn [$var]
@@ -74,8 +116,8 @@
 
 ;; [Resources]
 (do-template [<name> <output-tag> <input-class> <output-class>]
-  (let [input-type (&type/Data$ <input-class> (&/|list))
-        output-type (&type/Data$ <output-class> (&/|list))]
+  (let [input-type (&type/Data$ <input-class> &/Nil$)
+        output-type (&type/Data$ <output-class> &/Nil$)]
     (defn <name> [analyse exo-type x y]
       (|do [=x (&&/analyse-1 analyse input-type x)
             =y (&&/analyse-1 analyse input-type y)
@@ -157,12 +199,15 @@
 
 (defn analyse-jvm-invokestatic [analyse exo-type class method classes args]
   (|do [class-loader &/loader
-        =return (&host/lookup-static-method class-loader class method classes)
+        =return+exceptions (&host/lookup-static-method class-loader class method classes)
+        :let [[=return exceptions] =return+exceptions]
+        ;; :let [_ (prn 'analyse-jvm-invokestatic (&/adt->text =return+exceptions))]
+        _ (ensure-catching exceptions)
         ;; :let [_ (matchv ::M/objects [=return]
-        ;;           [[&/$DataT _return-class (&/|list)]]
+        ;;           [[&/$DataT _return-class &/Nil$]]
         ;;           (prn 'analyse-jvm-invokestatic class method _return-class))]
         =args (&/map2% (fn [_class _arg]
-                         (&&/analyse-1 analyse (&type/Data$ _class (&/|list)) _arg))
+                         (&&/analyse-1 analyse (&type/Data$ _class &/Nil$) _arg))
                        classes
                        args)
         :let [output-type =return]
@@ -179,11 +224,16 @@
 (do-template [<name> <tag>]
   (defn <name> [analyse exo-type class method classes object args]
     (|do [class-loader &/loader
-          =return (&host/lookup-virtual-method class-loader class method classes)
-          =object (&&/analyse-1 analyse (&type/Data$ class (&/|list)) object)
-          =args (&/map2% (fn [c o] (&&/analyse-1 analyse (&type/Data$ c (&/|list)) o))
+          =return+exceptions (&host/lookup-virtual-method class-loader class method classes)
+          ;; :let [_ (prn '<name> [class method] (&/adt->text =return+exceptions))]
+          :let [[=return exceptions] =return+exceptions]
+          _ (ensure-catching exceptions)
+          =object (&&/analyse-1 analyse (&type/Data$ class &/Nil$) object)
+          =args (&/map2% (fn [c o] (&&/analyse-1 analyse (&type/Data$ c &/Nil$) o))
                          classes args)
           :let [output-type =return]
+          ;; :let [_ (prn '<name> [class method] '=return (&type/show-type =return))]
+          ;; :let [_ (prn '<name> '(as-otype+ output-type) (&type/show-type (as-otype+ output-type)))]
           _ (&type/check exo-type (as-otype+ output-type))]
       (return (&/|list (&/T (&/V <tag> (&/T class method classes =object =args)) output-type)))))
 
@@ -193,12 +243,15 @@
 
 (defn analyse-jvm-invokespecial [analyse exo-type class method classes object args]
   (|do [class-loader &/loader
-        =return (if (= "<init>" method)
-                  (return &type/Unit)
-                  (&host/lookup-virtual-method class-loader class method classes))
-        =object (&&/analyse-1 analyse (&type/Data$ class (&/|list)) object)
+        =return+exceptions (if (= "<init>" method)
+                             (return (&/T &type/Unit &/Nil$))
+                             (&host/lookup-virtual-method class-loader class method classes))
+        :let [[=return exceptions] =return+exceptions]
+        ;; :let [_ (prn 'analyse-jvm-invokespecial (&/adt->text =return+exceptions))]
+        _ (ensure-catching exceptions)
+        =object (&&/analyse-1 analyse (&type/Data$ class &/Nil$) object)
         =args (&/map2% (fn [c o]
-                         (&&/analyse-1 analyse (&type/Data$ c (&/|list)) o))
+                         (&&/analyse-1 analyse (&type/Data$ c &/Nil$) o))
                        classes args)
         :let [output-type =return]
         _ (&type/check exo-type (as-otype+ output-type))]
@@ -212,21 +265,21 @@
     (return (&/|list (&/T (&/V &&/$jvm-null? =object) output-type)))))
 
 (defn analyse-jvm-null [analyse exo-type]
-  (|do [:let [output-type (&type/Data$ "null" (&/|list))]
+  (|do [:let [output-type (&type/Data$ "null" &/Nil$)]
         _ (&type/check exo-type output-type)]
     (return (&/|list (&/T (&/V &&/$jvm-null nil) output-type)))))
 
 (defn analyse-jvm-new [analyse exo-type class classes args]
   (|do [class-loader &/loader
         =return (&host/lookup-constructor class-loader class classes)
-        =args (&/map2% (fn [c o] (&&/analyse-1 analyse (&type/Data$ c (&/|list)) o))
+        =args (&/map2% (fn [c o] (&&/analyse-1 analyse (&type/Data$ c &/Nil$) o))
                        classes args)
-        :let [output-type (&type/Data$ class (&/|list))]
+        :let [output-type (&type/Data$ class &/Nil$)]
         _ (&type/check exo-type output-type)]
     (return (&/|list (&/T (&/V &&/$jvm-new (&/T class classes =args)) output-type)))))
 
 (do-template [<class> <new-name> <new-tag> <load-name> <load-tag> <store-name> <store-tag>]
-  (let [elem-type (&type/Data$ <class> (&/|list))
+  (let [elem-type (&type/Data$ <class> &/Nil$)
         array-type (&type/Data$ "Array" (&/|list elem-type))]
     (defn <new-name> [analyse length]
       (return (&/|list (&/T (&/V <new-tag> length) array-type))))
@@ -252,24 +305,24 @@
   )
 
 (defn analyse-jvm-anewarray [analyse class length]
-  (let [elem-type (&type/Data$ class (&/|list))
+  (let [elem-type (&type/Data$ class &/Nil$)
         array-type (&type/Data$ "Array" (&/|list elem-type))]
     (return (&/|list (&/T (&/V &&/$jvm-anewarray (&/T class length)) array-type)))))
 
 (defn analyse-jvm-aaload [analyse class array idx]
-  (let [elem-type (&type/Data$ class (&/|list))
+  (let [elem-type (&type/Data$ class &/Nil$)
         array-type (&type/Data$ "Array" (&/|list elem-type))]
     (|do [=array (&&/analyse-1 analyse array-type array)]
       (return (&/|list (&/T (&/V &&/$jvm-aaload (&/T class =array idx)) elem-type))))))
 
 (defn analyse-jvm-aastore [analyse class array idx elem]
-  (let [elem-type (&type/Data$ class (&/|list))
+  (let [elem-type (&type/Data$ class &/Nil$)
         array-type (&type/Data$ "Array" (&/|list elem-type))]
     (|do [=array (&&/analyse-1 analyse array-type array)
           =elem (&&/analyse-1 analyse elem-type elem)]
       (return (&/|list (&/T (&/V &&/$jvm-aastore (&/T class =array idx =elem)) array-type))))))
 
-(let [length-type (&type/Data$ "java.lang.Long" (&/|list))]
+(let [length-type (&type/Data$ "java.lang.Long" &/Nil$)]
   (defn analyse-jvm-arraylength [analyse array]
     (&type/with-var
       (fn [$var]
@@ -353,11 +406,11 @@
                                    =method-body (&/with-scope (str ?name "_" ?idx)
                                                   (&/fold (fn [body* input*]
                                                             (|let [[iname itype] input*]
-                                                              (&&env/with-local iname (&type/Data$ (as-otype itype) (&/|list))
+                                                              (&&env/with-local iname (&type/Data$ (as-otype itype) &/Nil$)
                                                                 body*)))
                                                           (if (= "void" ?method-output)
                                                             (analyse-1+ analyse ?method-body)
-                                                            (&&/analyse-1 analyse (&type/Data$ (as-otype ?method-output) (&/|list)) ?method-body))
+                                                            (&&/analyse-1 analyse (&type/Data$ (as-otype ?method-output) &/Nil$) ?method-body))
                                                           (&/|reverse (if (:static? =method-modifiers)
                                                                         =method-inputs
                                                                         (&/Cons$ (&/T "this" ?super-class)
@@ -396,7 +449,7 @@
         _ (compile-token (&/V &&/$jvm-class (&/T ?name ?super-class ?interfaces =fields =methods)))
         ;; :let [_ (prn 'analyse-jvm-class ?name ?super-class)]
         ]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-jvm-interface [analyse compile-token name supers methods]
   (|do [=methods (&/map% (fn [method]
@@ -417,19 +470,21 @@
                              (fail (str "[Analyser Error] Invalid method signature: " (&/show-ast method)))))
                          methods)
         _ (compile-token (&/V &&/$jvm-interface (&/T name supers =methods)))]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-jvm-try [analyse exo-type ?body ?catches+?finally]
   (|do [:let [[?catches ?finally] ?catches+?finally]
-        =body (&&/analyse-1 analyse exo-type ?body)
         =catches (&/map% (fn [[?ex-class ?ex-arg ?catch-body]]
-                           (|do [=catch-body (&&env/with-local ?ex-arg (&type/Data$ ?ex-class (&/|list))
+                           (|do [=catch-body (&&env/with-local ?ex-arg (&type/Data$ ?ex-class &/Nil$)
                                                (&&/analyse-1 analyse exo-type ?catch-body))
                                  idx &&env/next-local-idx]
                              (return (&/T ?ex-class idx =catch-body))))
                          ?catches)
+        :let [catched-exceptions (&/|map #(aget % 0) =catches)]
+        =body (with-catches catched-exceptions
+                (&&/analyse-1 analyse exo-type ?body))
         =finally (|case ?finally
-                   (&/$None)           (return (&/V &/$None nil))
+                   (&/$None)           (return &/None$)
                    (&/$Some ?finally*) (|do [=finally (analyse-1+ analyse ?finally*)]
                                          (return (&/V &/$Some =finally))))]
     (return (&/|list (&/T (&/V &&/$jvm-try (&/T =body =catches =finally)) exo-type)))))
@@ -437,7 +492,7 @@
 (defn analyse-jvm-throw [analyse exo-type ?ex]
   (|do [=ex (analyse-1+ analyse ?ex)
         :let [[_obj _type] =ex]
-        _ (&type/check (&type/Data$ "java.lang.Throwable" (&/|list)) _type)]
+        _ (&type/check (&type/Data$ "java.lang.Throwable" &/Nil$) _type)]
     (return (&/|list (&/T (&/V &&/$jvm-throw =ex) &type/$Void)))))
 
 (do-template [<name> <tag>]
@@ -453,9 +508,9 @@
   )
 
 (do-template [<name> <tag> <from-class> <to-class>]
-  (let [output-type (&type/Data$ <to-class> (&/|list))]
+  (let [output-type (&type/Data$ <to-class> &/Nil$)]
     (defn <name> [analyse exo-type ?value]
-      (|do [=value (&&/analyse-1 analyse (&type/Data$ <from-class> (&/|list)) ?value)
+      (|do [=value (&&/analyse-1 analyse (&type/Data$ <from-class> &/Nil$) ?value)
             _ (&type/check exo-type output-type)]
         (return (&/|list (&/T (&/V <tag> =value) output-type))))))
 
@@ -480,9 +535,9 @@
   )
 
 (do-template [<name> <tag> <from-class> <to-class>]
-  (let [output-type (&type/Data$ <to-class> (&/|list))]
+  (let [output-type (&type/Data$ <to-class> &/Nil$)]
     (defn <name> [analyse exo-type ?value]
-      (|do [=value (&&/analyse-1 analyse (&type/Data$ <from-class> (&/|list)) ?value)
+      (|do [=value (&&/analyse-1 analyse (&type/Data$ <from-class> &/Nil$) ?value)
             _ (&type/check exo-type output-type)]
         (return (&/|list (&/T (&/V <tag> =value) output-type))))))
 
@@ -501,9 +556,11 @@
   analyse-jvm-lushr &&/$jvm-lushr "java.lang.Long"    "java.lang.Integer"
   )
 
-(defn analyse-jvm-program [analyse compile-token ?args ?body]
-  (|do [=body (&/with-scope ""
-                (&&env/with-local ?args (&/V &/$AppT (&/T &type/List &type/Text))
-                  (&&/analyse-1 analyse (&/V &/$AppT (&/T &type/IO &type/Unit)) ?body)))
-        _ (compile-token (&/V &&/$jvm-program =body))]
-    (return (&/|list))))
+(let [input-type (&type/App$ &type/List &type/Text)
+      output-type (&type/App$ &type/IO &type/Unit)]
+  (defn analyse-jvm-program [analyse compile-token ?args ?body]
+    (|do [=body (&/with-scope ""
+                  (&&env/with-local ?args input-type
+                    (&&/analyse-1 analyse output-type ?body)))
+          _ (compile-token (&/V &&/$jvm-program =body))]
+      (return &/Nil$))))
diff --git a/src/lux/analyser/lux.clj b/src/lux/analyser/lux.clj
index 6205adccb..4a03c4848 100644
--- a/src/lux/analyser/lux.clj
+++ b/src/lux/analyser/lux.clj
@@ -59,7 +59,7 @@
                                   (|do [:let [=var* (next-bound-type tuple-type)]
                                         _ (&type/set-var iid =var*)
                                         tuple-type* (&type/clean $var tuple-type)]
-                                    (return (&type/Univ$ (&/|list) tuple-type*)))
+                                    (return (&type/Univ$ &/Nil$ tuple-type*)))
 
                                   _
                                   (&type/clean $var tuple-type))]
@@ -110,7 +110,7 @@
   (|do [output (with-attempt
                  (|case ?values
                    (&/$Nil)
-                   (analyse-tuple analyse (&/V &/$Right exo-type) (&/|list))
+                   (analyse-tuple analyse (&/V &/$Right exo-type) &/Nil$)
 
                    (&/$Cons ?value (&/$Nil))
                    (analyse exo-type ?value)
@@ -155,7 +155,7 @@
                                   (|do [:let [=var* (next-bound-type variant-type)]
                                         _ (&type/set-var iid =var*)
                                         variant-type* (&type/clean $var variant-type)]
-                                    (return (&type/Univ$ (&/|list) variant-type*)))
+                                    (return (&type/Univ$ &/Nil$ variant-type*)))
 
                                   _
                                   (&type/clean $var variant-type))
@@ -291,7 +291,7 @@
                                                 (&/T register* (&/Cons$ frame* new-inner))))
                                             (&/T (or (->> top-outer (&/get$ &/$locals)  (&/get$ &/$mappings) (&/|get name))
                                                      (->> top-outer (&/get$ &/$closure) (&/get$ &/$mappings) (&/|get name)))
-                                                 (&/|list))
+                                                 &/Nil$)
                                             (&/|reverse inner) scopes)]
               ((|do [_ (&type/check exo-type (&&/expr-type* =local))]
                  (return (&/|list =local)))
@@ -313,7 +313,7 @@
           _ (&type/check exo-type fun-type)
           ;; :let [_ (prn 'analyse-apply*/_1 'SUCCESS (str "(_ " (->> ?args (&/|map &/show-ast) (&/|interpose " ") (&/fold str "")) ")"))]
           ]
-      (return (&/T fun-type (&/|list))))
+      (return (&/T fun-type &/Nil$)))
     
     (&/$Cons ?arg ?args*)
     (|do [?fun-type* (&type/actual-type fun-type)]
@@ -416,7 +416,7 @@
                                             _ (&type/set-var iid =input*)
                                             =output* (&type/clean $input =output)
                                             =output** (&type/clean $output =output*)]
-                                        (return (&type/Univ$ (&/|list) (embed-inferred-input =input* =output**))))
+                                        (return (&type/Univ$ &/Nil$ (embed-inferred-input =input* =output**))))
 
                                       _
                                       (|do [=output* (&type/clean $input =output)
@@ -490,7 +490,7 @@
                 ;; :let [_ (println 'analyse-def/ALIAS (str module-name ";" ?name) '=> (str ?r-module ";" ?r-name))
                 ;;       _ (println)]
                 ]
-            (return (&/|list)))
+            (return &/Nil$))
 
           _
           (do ;; (println 'DEF (str module-name ";" ?name))
@@ -505,7 +505,7 @@
                           [def-analysis def-type] =value
                           _ (println 'DEF (str module-name ";" ?name) ;; (&type/show-type def-type)
                                      )]]
-                (return (&/|list)))))
+                (return &/Nil$))))
         ))))
 
 (defn analyse-declare-macro [analyse compile-token ?name]
@@ -515,7 +515,7 @@
         _ (compile-token (&/V &&/$declare-macro (&/T module-name ?name)))
         ;; :let [_ (prn 'analyse-declare-macro ?name "2")]
         ]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-declare-tags [tags type-name]
   (|do [module-name &/get-module-name
@@ -524,7 +524,7 @@
         ;; :let [_ (prn 'analyse-declare-tags (&/ident->text (&/T module-name type-name)) (&/->seq tags) (&/adt->text def-data))]
         def-type (&&module/ensure-type-def def-data)
         _ (&&module/declare-tags module-name tags def-type)]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-import [analyse compile-module compile-token path]
   ;; (prn 'analyse-import path)
@@ -537,17 +537,17 @@
            ;; :let [_ (prn 'analyse-import module-name path already-compiled?)]
            _ (&&module/add-import path)
            _ (&/when% (not already-compiled?) (compile-module path))]
-       (return (&/|list))))))
+       (return &/Nil$)))))
 
 (defn analyse-export [analyse compile-token name]
   (|do [module-name &/get-module-name
         _ (&&module/export module-name name)]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-alias [analyse compile-token ex-alias ex-module]
   (|do [module-name &/get-module-name
         _ (&&module/alias module-name ex-alias ex-module)]
-    (return (&/|list))))
+    (return &/Nil$)))
 
 (defn analyse-check [analyse eval! exo-type ?type ?value]
   (|do [=type (&&/analyse-1 analyse &type/Type ?type)
diff --git a/src/lux/analyser/module.clj b/src/lux/analyser/module.clj
index 97365ba08..deb6be69e 100644
--- a/src/lux/analyser/module.clj
+++ b/src/lux/analyser/module.clj
@@ -27,7 +27,7 @@
    ;; "lux;defs"
    (&/|table)
    ;; "lux;imports"
-   (&/|list)
+   &/Nil$
    ;; "lux;tags"
    (&/|table)
    ;; "lux;types"
diff --git a/src/lux/analyser/record.clj b/src/lux/analyser/record.clj
index 0f860888b..ddc9616fd 100644
--- a/src/lux/analyser/record.clj
+++ b/src/lux/analyser/record.clj
@@ -16,7 +16,7 @@
   "(-> (List (, Syntax Syntax)) (Lux (List Syntax)))"
   (|do [[tag-group tag-type] (|case pairs
                                (&/$Nil)
-                               (return (&/T (&/|list) &type/Unit))
+                               (return (&/T &/Nil$ &type/Unit))
                                
                                (&/$Cons [[_ (&/$TagS tag1)] _] _)
                                (|do [[module name] (&&/resolved-ident tag1)
diff --git a/src/lux/base.clj b/src/lux/base.clj
index c0f28f519..aefa0cf4c 100644
--- a/src/lux/base.clj
+++ b/src/lux/base.clj
@@ -84,7 +84,8 @@
 (deftags
   ["writer"
    "loader"
-   "classes"])
+   "classes"
+   "catching"])
 
 ;; Compiler
 (deftags
@@ -179,13 +180,13 @@
 (defmacro |list [& elems]
   (reduce (fn [tail head]
             `(V $Cons (T ~head ~tail)))
-          `(V $Nil nil)
+          `Nil$
           (reverse elems)))
 
 (defmacro |table [& elems]
   (reduce (fn [table [k v]]
             `(|put ~k ~v ~table))
-          `(|list)
+          `Nil$
           (reverse (partition 2 elems))))
 
 (defn |get [slot table]
@@ -201,7 +202,7 @@
 (defn |put [slot value table]
   (|case table
     ($Nil)
-    (V $Cons (T (T slot value) (V $Nil nil)))
+    (V $Cons (T (T slot value) Nil$))
     
     ($Cons [k v] table*)
     (if (.equals ^Object k slot)
@@ -344,7 +345,7 @@
     (if (p x)
       (|let [[pre post] (|split-with p xs*)]
         (T (Cons$ x pre) post))
-      (T (V $Nil nil) xs))))
+      (T Nil$ xs))))
 
 (defn |contains? [k table]
   (|case table
@@ -355,6 +356,14 @@
     (or (.equals ^Object k k*)
         (|contains? k table*))))
 
+(defn |member? [x xs]
+  (|case xs
+    ($Nil)
+    false
+
+    ($Cons x* xs*)
+    (or (= x x*) (|member? x xs*))))
+
 (defn fold [f init xs]
   (|case xs
     ($Nil)
@@ -386,7 +395,7 @@
 (let [|range* (fn |range* [from to]
                 (if (< from to)
                   (V $Cons (T from (|range* (inc from) to)))
-                  (V $Nil nil)))]
+                  Nil$))]
   (defn |range [n]
     (|range* 0 n)))
 
@@ -404,12 +413,12 @@
     (V $Cons (T (T x y) (zip2 xs* ys*)))
 
     [_ _]
-    (V $Nil nil)))
+    Nil$))
 
 (defn |keys [plist]
   (|case plist
     ($Nil)
-    (|list)
+    Nil$
     
     ($Cons [k v] plist*)
     (Cons$ k (|keys plist*))))
@@ -417,7 +426,7 @@
 (defn |vals [plist]
   (|case plist
     ($Nil)
-    (|list)
+    Nil$
     
     ($Cons [k v] plist*)
     (Cons$ v (|vals plist*))))
@@ -448,7 +457,7 @@
   flat-map% |++)
 
 (defn list-join [xss]
-  (fold |++ (V $Nil nil) xss))
+  (fold |++ Nil$ xss))
 
 (defn |as-pairs [xs]
   (|case xs
@@ -456,12 +465,12 @@
     (V $Cons (T (T x y) (|as-pairs xs*)))
 
     _
-    (V $Nil nil)))
+    Nil$))
 
 (defn |reverse [xs]
   (fold (fn [tail head]
           (Cons$ head tail))
-        (|list)
+        Nil$
         xs))
 
 (defn assert! [test message]
@@ -497,7 +506,7 @@
   (try-all% (|list (|do [head monad
                          tail (repeat% monad)]
                      (return (Cons$ head tail)))
-                   (return (|list)))))
+                   (return Nil$))))
 
 (defn exhaust% [step]
   (fn [state]
@@ -580,6 +589,7 @@
           (try (.invoke define-class this (to-array [class-name bytecode (int 0) (int (alength bytecode))]))
             (catch java.lang.reflect.InvocationTargetException e
               (prn 'InvocationTargetException (.getCause e))
+              (prn 'memory-class-loader/findClass class-name (get @store class-name))
               (throw e)))
           (do (prn 'memory-class-loader/store class-name (keys @store))
             (throw (IllegalStateException. (str "[Class Loader] Unknown class: " class-name)))))))))
@@ -591,7 +601,10 @@
      ;; "lux;loader"
      (memory-class-loader store)
      ;; "lux;classes"
-     store)))
+     store
+     ;; "lux;catching"
+     Nil$
+     )))
 
 (defn init-state [_]
   (T ;; "lux;source"
@@ -601,11 +614,11 @@
    ;; "lux;modules"
    (|table)
    ;; "lux;envs"
-   (|list)
+   Nil$
    ;; "lux;types"
    +init-bindings+
    ;; "lux;expected"
-   (V $VariantT (|list))
+   (V $VariantT Nil$)
    ;; "lux;seed"
    0
    ;; "lux;eval?"
@@ -671,13 +684,13 @@
 
 (defn ->list [seq]
   (if (empty? seq)
-    (|list)
+    Nil$
     (Cons$ (first seq) (->list (rest seq)))))
 
 (defn |repeat [n x]
   (if (> n 0)
     (Cons$ x (|repeat (dec n) x))
-    (|list)))
+    Nil$))
 
 (def get-module-name
   (fn [state]
@@ -830,7 +843,7 @@
       (return (Cons$ z zs)))
 
     [($Nil) ($Nil)]
-    (return (V $Nil nil))
+    (return Nil$)
 
     [_ _]
     (fail "Lists don't match in size.")))
@@ -841,7 +854,7 @@
     (Cons$ (f x y) (map2 f xs* ys*))
 
     [_ _]
-    (V $Nil nil)))
+    Nil$))
 
 (defn fold2 [f init xs ys]
   (|case [xs ys]
diff --git a/src/lux/compiler/cache.clj b/src/lux/compiler/cache.clj
index e47da2678..3532cf843 100644
--- a/src/lux/compiler/cache.clj
+++ b/src/lux/compiler/cache.clj
@@ -92,7 +92,7 @@
                                             (|do [content (&&io/read-file (str &&/input-dir "/" _import ".lux"))]
                                               (load _import (hash content) compile-module)))
                                           (if (= [""] imports)
-                                            (&/|list)
+                                            &/Nil$
                                             (&/->list imports)))]
                         (if (->> loads &/->seq (every? true?))
                           (do (doseq [^File file (seq (.listFiles (File. module-path)))
@@ -109,7 +109,7 @@
                                   ;;        (string/split (get-field &/tags-field module-meta) (re-pattern (java.util.regex.Pattern/quote &&/tag-group-separator))))
                                   tag-groups (let [all-tags (get-field &/tags-field module-meta)]
                                                (if (= "" all-tags)
-                                                 (&/|list)
+                                                 &/Nil$
                                                  (-> all-tags
                                                      (string/split (re-pattern (java.util.regex.Pattern/quote &&/tag-group-separator)))
                                                      (->> (map (fn [_group]
@@ -149,7 +149,7 @@
                                                       (return nil)))
                                                   ))
                                               (if (= [""] defs)
-                                                (&/|list)
+                                                &/Nil$
                                                 (&/->list defs)))
                                     _ (&/map% (fn [group]
                                                 (|let [[_type _tags] group]
diff --git a/src/lux/compiler/type.clj b/src/lux/compiler/type.clj
index 6c128df80..00e66410f 100644
--- a/src/lux/compiler/type.clj
+++ b/src/lux/compiler/type.clj
@@ -33,7 +33,7 @@
 
 (def ^:private $Nil
   "Analysis"
-  (variant$ &/$Nil (tuple$ (&/|list))))
+  (variant$ &/$Nil (tuple$ &/Nil$)))
 
 (defn ^:private Cons$ [head tail]
   "(-> Analysis Analysis Analysis)"
diff --git a/src/lux/host.clj b/src/lux/host.clj
index 8d6135d64..9137f3874 100644
--- a/src/lux/host.clj
+++ b/src/lux/host.clj
@@ -32,7 +32,7 @@
       &type/Unit
       (&type/Data$ (str (reduce str "" (repeat (int (/ (count arr-level) 2)) "["))
                         base)
-                   (&/|list))
+                   &/Nil$)
       )))
 
 (defn ^:private method->type [^Method method]
@@ -115,7 +115,7 @@
                                                             args
                                                             (&/|map #(.getName ^Class %) param-types)))))]
                              =method))]
-      (return (method->type method))
+      (return (&/T (method->type method) (->> method .getExceptionTypes &/->list (&/|map #(.getName %)))))
       (fail (str "[Host Error] Method does not exist: " target "." method-name))))
 
   lookup-static-method  true
diff --git a/src/lux/parser.clj b/src/lux/parser.clj
index dbd6ca2c5..516b6a947 100644
--- a/src/lux/parser.clj
+++ b/src/lux/parser.clj
@@ -17,7 +17,7 @@
           token &lexer/lex]
       (|case token
         [meta [<close-token> _]]
-        (return (&/V <tag> (&/fold &/|++ (&/|list) elems)))
+        (return (&/V <tag> (&/fold &/|++ &/Nil$ elems)))
         
         _
         (fail (str "[Parser Error] Unbalanced " <description> ".")))))
@@ -29,7 +29,7 @@
 (defn ^:private parse-record [parse]
   (|do [elems* (&/repeat% parse)
         token &lexer/lex
-        :let [elems (&/fold &/|++ (&/|list) elems*)]]
+        :let [elems (&/fold &/|++ &/Nil$ elems*)]]
     (|case token
       [meta (&lexer/$Close_Brace _)]
       (if (even? (&/|length elems))
@@ -45,10 +45,10 @@
         :let [[meta token*] token]]
     (|case token*
       (&lexer/$White_Space _)
-      (return (&/|list))
+      (return &/Nil$)
 
       (&lexer/$Comment _)
-      (return (&/|list))
+      (return &/Nil$)
       
       (&lexer/$Bool ?value)
       (return (&/|list (&/T meta (&/V &/$BoolS (Boolean/parseBoolean ?value)))))
diff --git a/src/lux/type.clj b/src/lux/type.clj
index 0da579cf4..8a1e11bed 100644
--- a/src/lux/type.clj
+++ b/src/lux/type.clj
@@ -23,7 +23,7 @@
     _
     false))
 
-(def ^:private empty-env (&/V &/$Nil nil))
+(def ^:private empty-env &/Nil$)
 (defn Data$ [name params]
   (&/V &/$DataT (&/T name params)))
 (defn Bound$ [idx]
@@ -46,13 +46,13 @@
   (&/V &/$NamedT (&/T name type)))
 
 
-(def Bool (Named$ (&/T "lux" "Bool") (Data$ "java.lang.Boolean" (&/|list))))
-(def Int (Named$ (&/T "lux" "Int") (Data$ "java.lang.Long" (&/|list))))
-(def Real (Named$ (&/T "lux" "Real") (Data$ "java.lang.Double" (&/|list))))
-(def Char (Named$ (&/T "lux" "Char") (Data$ "java.lang.Character" (&/|list))))
-(def Text (Named$ (&/T "lux" "Text") (Data$ "java.lang.String" (&/|list))))
-(def Unit (Named$ (&/T "lux" "Unit") (Tuple$ (&/|list))))
-(def $Void (Named$ (&/T "lux" "Void") (Variant$ (&/|list))))
+(def Bool (Named$ (&/T "lux" "Bool") (Data$ "java.lang.Boolean" &/Nil$)))
+(def Int (Named$ (&/T "lux" "Int") (Data$ "java.lang.Long" &/Nil$)))
+(def Real (Named$ (&/T "lux" "Real") (Data$ "java.lang.Double" &/Nil$)))
+(def Char (Named$ (&/T "lux" "Char") (Data$ "java.lang.Character" &/Nil$)))
+(def Text (Named$ (&/T "lux" "Text") (Data$ "java.lang.String" &/Nil$)))
+(def Unit (Named$ (&/T "lux" "Unit") (Tuple$ &/Nil$)))
+(def $Void (Named$ (&/T "lux" "Void") (Variant$ &/Nil$)))
 (def Ident (Named$ (&/T "lux" "Ident") (Tuple$ (&/|list Text Text))))
 
 (def IO
@@ -221,11 +221,14 @@
           (Tuple$
            (&/|list
             ;; "lux;writer"
-            (Data$ "org.objectweb.asm.ClassWriter" (&/|list))
+            (Data$ "org.objectweb.asm.ClassWriter" &/Nil$)
             ;; "lux;loader"
-            (Data$ "java.lang.ClassLoader" (&/|list))
+            (Data$ "java.lang.ClassLoader" &/Nil$)
             ;; "lux;classes"
-            (Data$ "clojure.lang.Atom" (&/|list))))))
+            (Data$ "clojure.lang.Atom" &/Nil$)
+            ;; "lux;catching"
+            (App$ List Text)
+            ))))
 
 (def DefData*
   (Univ$ empty-env
@@ -367,7 +370,7 @@
     (let [id (->> state (&/get$ &/$type-vars) (&/get$ &/$counter))]
       (return* (&/update$ &/$type-vars #(->> %
                                              (&/update$ &/$counter inc)
-                                             (&/update$ &/$mappings (fn [ms] (&/|put id (&/V &/$None nil) ms))))
+                                             (&/update$ &/$mappings (fn [ms] (&/|put id &/None$ ms))))
                           state)
                id))))
 
@@ -396,7 +399,7 @@
                                        (|case ?type*
                                          (&/$VarT ?id*)
                                          (if (.equals ^Object id ?id*)
-                                           (return (&/T ?id (&/V &/$None nil)))
+                                           (return (&/T ?id &/None$))
                                            (return binding))
 
                                          _
@@ -465,7 +468,7 @@
       (&/T ??out (&/Cons$ ?in ?args)))
 
     _
-    (&/T type (&/|list))))
+    (&/T type &/Nil$)))
 
 (defn ^:private unravel-app [fun-type]
   (|case fun-type
@@ -474,7 +477,7 @@
       (&/T ?fun-type (&/|++ ?args (&/|list ?right))))
 
     _
-    (&/T fun-type (&/|list))))
+    (&/T fun-type &/Nil$)))
 
 (defn show-type [^objects type]
   (|case type
@@ -581,7 +584,7 @@
   (|let [[e a] k]
     (|case fixpoints
       (&/$Nil)
-      (&/V &/$None nil)
+      &/None$
 
       (&/$Cons [[e* a*] v*] fixpoints*)
       (if (and (type= e e*)
@@ -674,7 +677,7 @@
 
 (def ^:private primitive-types #{"boolean" "byte" "short" "int" "long" "float" "double" "char"})
 
-(def ^:private init-fixpoints (&/|list))
+(def ^:private init-fixpoints &/Nil$)
 
 (defn ^:private check* [class-loader fixpoints invariant?? expected actual]
   (if (clojure.lang.Util/identical expected actual)
@@ -689,14 +692,14 @@
                          (return* state* (&/V &/$Some ebound))
 
                          (&/$Left _)
-                         (return* state (&/V &/$None nil))))
+                         (return* state &/None$)))
               abound (fn [state]
                        (|case ((deref ?aid) state)
                          (&/$Right state* abound)
                          (return* state* (&/V &/$Some abound))
 
                          (&/$Left _)
-                         (return* state (&/V &/$None nil))))]
+                         (return* state &/None$)))]
           (|case [ebound abound]
             [(&/$None _) (&/$None _)]
             (|do [_ (set-var ?eid actual)]
@@ -873,6 +876,10 @@
                 (return (&/T fixpoints nil)))
 
               (and (not invariant??)
+                   ;; (do (println '[Data Data] [e!name a!name]
+                   ;;              [(str "(" (->> e!params (&/|map show-type) (&/|interpose " ") (&/fold str "")) ")")
+                   ;;               (str "(" (->> a!params (&/|map show-type) (&/|interpose " ") (&/fold str "")) ")")])
+                   ;;   true)
                    (.isAssignableFrom (Class/forName e!name true class-loader) (Class/forName a!name true class-loader)))
               (return (&/T fixpoints nil))