- List ranges can now be generated backwards.

3 files changed, 34 insertions, 18 deletions

diff --git a/stdlib/source/lux/data/coll/list.lux b/stdlib/source/lux/data/coll/list.lux
index b9b743b2c..f6c19dcb9 100644
--- a/stdlib/source/lux/data/coll/list.lux
+++ b/stdlib/source/lux/data/coll/list.lux
@@ -303,16 +303,21 @@
                            xs')]
       ($_ compose (sort < pre) (list x) (sort < post)))))
 
-(do-template [<name> <type> <comp> <inc>]
+(do-template [<name> <type> <lt> <inc> <gt> <dec>]
   [(def: #export (<name> from to)
      {#.doc "Generates an inclusive interval of values [from, to]."}
      (-> <type> <type> (List <type>))
-     (if (<comp> to from)
-       (list& from (<name> (<inc> from) to))
-       (list)))]
+     (cond (<lt> to from)
+           (list& from (<name> (<inc> from) to))
 
-  [i/range Int i/<= i/inc]
-  [n/range Nat n/<= n/inc]
+           (<gt> to from)
+           (list& from (<name> (<dec> from) to))
+
+           ## (= to from)
+           (list from)))]
+
+  [i/range Int i/< i/inc i/> i/dec]
+  [n/range Nat n/< n/inc n/> n/dec]
   )
 
 (def: #export (empty? xs)
diff --git a/stdlib/test/test/lux/control/region.lux b/stdlib/test/test/lux/control/region.lux
index a7a577ab5..fc1eb7edf 100644
--- a/stdlib/test/test/lux/control/region.lux
+++ b/stdlib/test/test/lux/control/region.lux
@@ -26,7 +26,7 @@
 (context: "Regions."
   (<| (times +100)
       (do @
-        [expected-clean-ups (|> r.nat (:: @ map (n/% +100)))]
+        [expected-clean-ups (|> r.nat (:: @ map (|>> (n/% +100) (n/max +1))))]
         ($_ seq
             (test "Clean-up functions are always run when region execution is done."
                   (thread.run
diff --git a/stdlib/test/test/lux/data/coll/list.lux b/stdlib/test/test/lux/data/coll/list.lux
index 729519823..578b652da 100644
--- a/stdlib/test/test/lux/data/coll/list.lux
+++ b/stdlib/test/test/lux/data/coll/list.lux
@@ -132,6 +132,8 @@
          other-size bounded-size
          other-sample (r.list other-size r.nat)
          separator r.nat
+         from (|> r.nat (:: @ map (n/% +10)))
+         to (|> r.nat (:: @ map (n/% +10)))
          #let [(^open) (&.Eq<List> number.Eq<Nat>)
                (^open "&/") &.Functor<List>]]
         ($_ seq
@@ -208,17 +210,26 @@
                             (&/map product.left enum-sample))
                          (= sample
                             (&/map product.right enum-sample)))))
+
+            (test "Ranges can be constructed forward and backwards."
+                  (and (let [(^open "list/") (&.Eq<List> number.Eq<Nat>)]
+                         (list/= (&.n/range from to)
+                                 (&.reverse (&.n/range to from))))
+                       (let [(^open "list/") (&.Eq<List> number.Eq<Int>)
+                             from (nat-to-int from)
+                             to (nat-to-int to)]
+                         (list/= (&.i/range from to)
+                                 (&.reverse (&.i/range to from))))))
             ))))
 
 ## TODO: Add again once new-luxc becomes the standard compiler.
-## (context: "Monad transformer"
-##   (let [lift (&.lift io.Monad<IO>)
-##         (^open "io/") io.Monad<IO>]
-##     (test "Can add list functionality to any monad."
-##           (|> (io.run (do (&.ListT io.Monad<IO>)
-##                         [a (lift (io/wrap 123))
-##                          b (wrap 456)]
-##                         (wrap (i/+ a b))))
-##               (case> (^ (list 579)) true
-##                      _              false)))
-##     ))
+(context: "Monad transformer"
+  (let [lift (&.lift io.Monad<IO>)
+        (^open "io/") io.Monad<IO>]
+    (test "Can add list functionality to any monad."
+          (|> (io.run (do (&.ListT io.Monad<IO>)
+                        [a (lift (io/wrap 123))
+                         b (wrap 456)]
+                        (wrap (i/+ a b))))
+              (case> (^ (list 579)) true
+                     _              false)))))