- Implemented ":share" macro for easier type-sharing when casting.

1 files changed, 25 insertions, 2 deletions

diff --git a/stdlib/source/lux/lang/type.lux b/stdlib/source/lux/lang/type.lux
index 96ea1a9b0..793d1c8be 100644
--- a/stdlib/source/lux/lang/type.lux
+++ b/stdlib/source/lux/lang/type.lux
@@ -10,7 +10,7 @@
              (coll [list #+ "list/" Functor<List> Monoid<List> Fold<List>]))
        [macro]
        (macro [code]
-              ["s" syntax #+ syntax:])
+              ["s" syntax #+ Syntax syntax:])
        ))
 
 ## [Utils]
@@ -351,7 +351,11 @@
       (wrap (list (` (.let [(~ g!value) (~ valueC)]
                        (..:log! (~ g!value)))))))))
 
-(syntax: #export (:cast {type-vars (s.tuple (p.some s.local-symbol))}
+(def: type-parameters
+  (Syntax (List Text))
+  (s.tuple (p.some s.local-symbol)))
+
+(syntax: #export (:cast {type-vars type-parameters}
                         input
                         output
                         {value (p.maybe s.any)})
@@ -364,3 +368,22 @@
       
       (#.Some value)
       (wrap (list (` ((~ casterC) (~ value))))))))
+
+(type: Typed
+  {#type Code
+   #expression Code})
+
+(def: typed
+  (Syntax Typed)
+  (s.record (p.seq s.any s.any)))
+
+(syntax: #export (:share {type-vars type-parameters}
+                         {exemplar typed}
+                         {computation typed})
+  (macro.with-gensyms [g!_]
+    (let [shareC (` (: (All [(~+ (list/map code.local-symbol type-vars))]
+                         (-> (~ (get@ #type exemplar))
+                             (~ (get@ #type computation))))
+                       (.function ((~ g!_) (~ g!_))
+                         (:assume (~ (get@ #expression computation))))))]
+      (wrap (list (` ((~ shareC) (~ (get@ #expression exemplar)))))))))