fix: Separate variable/discard patterns

boot/MiloneLang/ClosureConversion.fs

@@ -142,6 +142,7 @@ let declosurePat (pat, ctx) =
   match pat with
   | HPat.Lit _
   | HPat.Nil _
+  | HPat.Discard _
   | HPat.Nav _ ->
     pat, ctx
   | HPat.Ref (serial, _, _) ->

boot/MiloneLang/Helpers.fs

@@ -533,6 +533,8 @@ let rec patExtract (pat: HPat): Ty * Loc =
     litToTy lit, a
   | HPat.Nil (itemTy, a) ->
     tyList itemTy, a
+  | HPat.Discard (ty, a) ->
+    ty, a
   | HPat.Ref (_, ty, a) ->
     ty, a
   | HPat.Nav (_, _, ty, a) ->
@@ -558,6 +560,8 @@ let patMap (f: Ty -> Ty) (g: Loc -> Loc) (pat: HPat): HPat =
       HPat.Lit (lit, g a)
     | HPat.Nil (itemTy, a) ->
       HPat.Nil (f itemTy, g a)
+    | HPat.Discard (ty, a) ->
+      HPat.Discard (f ty, g a)
     | HPat.Ref (serial, ty, a) ->
       HPat.Ref (serial, f ty, g a)
     | HPat.Nav (pat, ident, ty, a) ->
@@ -582,6 +586,7 @@ let patNormalize pat =
   let rec go pat =
     match pat with
     | HPat.Lit _
+    | HPat.Discard _
     | HPat.Ref _
     | HPat.Nil _ ->
       [pat]

boot/MiloneLang/Mir.fs

@@ -215,9 +215,11 @@ let mirifyPatAs ctx endLabel pat serial expr loc =
 /// Determines if the pattern covers the whole.
 let mirifyPat ctx (endLabel: string) (pat: HPat) (expr: MExpr): bool * MirCtx =
   match pat with
-  | HPat.Ref ("_", _, _, _) ->
-    // Discard result.
+  | HPat.Discard _ ->
+    // Discard the result, which we know is pure.
+    // FIXME: This should be done in optimization?
     true, ctx
+
   | HPat.Lit (lit, loc) ->
     mirifyPatLit ctx endLabel lit expr loc
   | HPat.Nil (itemTy, loc) ->
@@ -270,6 +272,7 @@ let mirifyBlock ctx expr =
 let patsIsCovering pats =
   let rec go pat =
     match pat with
+    | HPat.Discard _
     | HPat.Ref _ ->
       // FIXME: unit-like variant patterns may not be covering
       true

boot/MiloneLang/NameRes.fs

@@ -411,6 +411,7 @@ let collectDecls (expr, ctx) =
   let rec goPat (pat, ctx) =
     match pat with
     | HPat.Lit _
+    | HPat.Discard _
     | HPat.Nav _
     | HPat.Nil _ ->
       pat, ctx
@@ -551,15 +552,13 @@ let primFromIdent ident =
 let onPat (pat: HPat, ctx: ScopeCtx) =
   match pat with
   | HPat.Lit _
+  | HPat.Discard _
   | HPat.Nil _ ->
     pat, ctx
 
   | HPat.Ref (varSerial, ty, loc)
     when ctx |> scopeCtxGetIdent varSerial = "_" ->
-    // Handle discard pattern.
-    let varDef = VarDef.Var ("_", ty, loc)
-    let ctx = ctx |> scopeCtxDefineVar varSerial varDef
-    HPat.Ref (varSerial, ty, loc), ctx
+    HPat.Discard (ty, loc), ctx
 
   | HPat.Ref (varSerial, ty, loc) ->
     let ident = ctx |> scopeCtxGetIdent varSerial

boot/MiloneLang/Types.fs

@@ -455,7 +455,10 @@ type HPat =
   /// `[]`
   | Nil
     of itemTy:Ty * Loc
-  /// Variable reference pattern or `_`.
+  /// `_`
+  | Discard
+    of Ty * Loc
+  /// Variable pattern.
   | Ref
     of VarSerial * Ty * Loc
   | Nav

boot/MiloneLang/Typing.fs

@@ -270,6 +270,8 @@ let inferPat ctx pat ty =
     let itemTy, ctx = ctx |> ctxFreshPatTy pat
     let ctx = unifyTy ctx loc ty (tyList itemTy)
     HPat.Nil (itemTy, loc), ctx
+  | HPat.Discard (_, loc) ->
+    HPat.Discard (ty, loc), ctx
   | HPat.Ref (varSerial, _, loc) ->
     inferPatRef ctx varSerial loc ty
   | HPat.Nav (l, r, _, loc) ->

boot/tests/errors/ty_errors/ty_errors.c

@@ -63,8 +63,8 @@ end_match_4:;
 #error 7:24 While unifying 'Con (Tuple,[Con (Tuple,[Con (Int,[]); Con (Int,[])]); Con (Int,[])])' and 'Con (Tuple,[Con (Tuple,[Con (Int,[]); Con (Str,[])]); Con (Int,[])])', failed to unify 'Con (Int,[])' and 'Con (Str,[])'.
 
 #line 13
-#error 13:17 Couldn't unify 'Meta (40,(12, 12))' and 'Con
-  (Fun,[Con (Fun,[Meta (40,(12, 12)); Meta (39,(12, 16))]); Meta (39,(12, 16))])' due to self recursion.
+#error 13:17 Couldn't unify 'Meta (39,(12, 12))' and 'Con
+  (Fun,[Con (Fun,[Meta (39,(12, 12)); Meta (38,(12, 16))]); Meta (38,(12, 16))])' due to self recursion.
 
 #line 15
 #error 15:3 While unifying 'Con (Int,[])' and 'Con (Tuple,[])', failed to unify 'Con (Int,[])' and 'Con (Tuple,[])'.

boot/tests/examples/MatchChecker/MatchChecker.c

@@ -184,7 +184,7 @@ struct IntSpace_Space_Tuple3;
 
 struct Space_ fun_12(void* env_3, int arg_5, struct Space_Space_Tuple2 arg_6);
 
-struct Space_ fun_28(struct Space_List* seconds_, struct Space_List* firsts_, struct String tag_2, struct Space_ spaceEmpty_, struct Space_ spaceFull_, int i_1, struct Space_ __14);
+struct Space_ fun_28(struct Space_List* seconds_, struct Space_List* firsts_, struct String tag_2, struct Space_ spaceEmpty_, struct Space_ spaceFull_, int i_1, struct Space_ arg_51);
 
 struct Space_ListSpace_ListStringSpace_Space_Tuple5;
 
@@ -220,7 +220,7 @@ struct Space_ fun_18(void* env_9, struct Ty_ arg_29);
 
 struct Space_ fun_19(void* env_10, int arg_31);
 
-struct Space_ thunk_2(struct Space_ itemSpace_, int arg_51);
+struct Space_ thunk_2(struct Space_ itemSpace_, int arg_52);
 
 struct Space_ fun_20(void* env_11, int arg_33);
 
@@ -238,27 +238,27 @@ struct Space_ fun_22(void* env_13, struct Pat_ arg_38);
 
 struct Space_ patsToSpace_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, struct Pat_List* pats_);
 
-struct Space_ fun_6(struct Space_ spaceFull_, int arg_52);
+struct Space_ fun_6(struct Space_ spaceFull_, int arg_53);
 
 struct Space_ fun_23(void* env_14, int arg_41);
 
-int testSpaceIsEmpty_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_53);
+int testSpaceIsEmpty_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_54);
 
 int fun_24(void* env_15, int arg_43);
 
-int fun_7(struct StringSpace_Tuple2 arg_54);
+int fun_7(struct StringSpace_Tuple2 arg_55);
 
 int fun_25(void* env_16, struct StringSpace_Tuple2 arg_44);
 
-int testSpaceToString_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_55);
+int testSpaceToString_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_56);
 
 int fun_26(void* env_17, int arg_45);
 
 struct BoolStringTuple2;
 
 struct Covering_Covering_Tuple2;
 
-int fun_8(struct Space_ spaceEmpty_, struct Space_ spaceFull_, struct StringTy_Pat_ListCovering_Tuple4 arg_56);
+int fun_8(struct Space_ spaceEmpty_, struct Space_ spaceFull_, struct StringTy_Pat_ListCovering_Tuple4 arg_57);
 
 int fun_27(void* env_18, struct StringTy_Pat_ListCovering_Tuple4 arg_46);
 
@@ -1236,7 +1236,7 @@ struct Space_ fun_12(void* env_3, int arg_5, struct Space_Space_Tuple2 arg_6) {
     return call_67;
 }
 
-struct Space_ fun_28(struct Space_List* seconds_, struct Space_List* firsts_, struct String tag_2, struct Space_ spaceEmpty_, struct Space_ spaceFull_, int i_1, struct Space_ __14) {
+struct Space_ fun_28(struct Space_List* seconds_, struct Space_List* firsts_, struct String tag_2, struct Space_ spaceEmpty_, struct Space_ spaceFull_, int i_1, struct Space_ arg_51) {
     struct IntSpace_Space_Tuple3 tuple_4;
     tuple_4.t0 = i_1;
     tuple_4.t1 = spaceEmpty_;
@@ -1540,7 +1540,7 @@ struct Space_ fun_19(void* env_10, int arg_31) {
     return call_113;
 }
 
-struct Space_ thunk_2(struct Space_ itemSpace_, int arg_51) {
+struct Space_ thunk_2(struct Space_ itemSpace_, int arg_52) {
     struct Space_ call_114 = spaceCtor_((struct String){.str = "nil", .len = 3}, NULL);
     struct Space_Tuple1 tuple_10;
     tuple_10.t0 = itemSpace_;
@@ -1698,7 +1698,7 @@ struct Space_ patsToSpace_(struct Space_ spaceEmpty_, struct Space_ spaceFull_,
     return call_135;
 }
 
-struct Space_ fun_6(struct Space_ spaceFull_, int arg_52) {
+struct Space_ fun_6(struct Space_ spaceFull_, int arg_53) {
     return spaceFull_;
 }
 
@@ -1708,7 +1708,7 @@ struct Space_ fun_23(void* env_14, int arg_41) {
     return call_136;
 }
 
-int testSpaceIsEmpty_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_53) {
+int testSpaceIsEmpty_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_54) {
     int call_137 = spaceIsEmpty_(spaceEmpty_);
     milone_assert(call_137, 455, 2);
     int call_138 = 0;
@@ -1791,9 +1791,9 @@ int fun_24(void* env_15, int arg_43) {
     return call_163;
 }
 
-int fun_7(struct StringSpace_Tuple2 arg_54) {
-    struct String expected_ = arg_54.t0;
-    struct Space_ space_10 = arg_54.t1;
+int fun_7(struct StringSpace_Tuple2 arg_55) {
+    struct String expected_ = arg_55.t0;
+    struct Space_ space_10 = arg_55.t1;
     struct String call_164 = spaceToString_(space_10);
     struct String actual_ = call_164;
     int match_33;
@@ -1817,7 +1817,7 @@ int fun_25(void* env_16, struct StringSpace_Tuple2 arg_44) {
     return call_166;
 }
 
-int testSpaceToString_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_55) {
+int testSpaceToString_(struct Space_ spaceEmpty_, struct Space_ spaceFull_, int arg_56) {
     struct StringSpace_Tuple2 tuple_16;
     tuple_16.t0 = (struct String){.str = "empty", .len = 5};
     tuple_16.t1 = spaceEmpty_;
@@ -1913,11 +1913,11 @@ struct Covering_Covering_Tuple2 {
     struct Covering_ t1;
 };
 
-int fun_8(struct Space_ spaceEmpty_, struct Space_ spaceFull_, struct StringTy_Pat_ListCovering_Tuple4 arg_56) {
-    struct String name_ = arg_56.t0;
-    struct Ty_ ty_2 = arg_56.t1;
-    struct Pat_List* pats_1 = arg_56.t2;
-    struct Covering_ covering_ = arg_56.t3;
+int fun_8(struct Space_ spaceEmpty_, struct Space_ spaceFull_, struct StringTy_Pat_ListCovering_Tuple4 arg_57) {
+    struct String name_ = arg_57.t0;
+    struct Ty_ ty_2 = arg_57.t1;
+    struct Pat_List* pats_1 = arg_57.t2;
+    struct Covering_ covering_ = arg_57.t3;
     struct Space_ call_177 = tyToSpace_(spaceFull_, ty_2);
     struct Space_ tySpace_ = call_177;
     struct Space_ call_178 = patsToSpace_(spaceEmpty_, spaceFull_, pats_1);

boot/tests/features/union_complex/union_complex.c

@@ -20,7 +20,7 @@ struct First_Second_Tuple2;
 
 struct First_Second_Tuple2List;
 
-struct First_ListSecond_ListTuple2 f_(struct First_Second_Tuple2List* __2);
+struct First_ListSecond_ListTuple2 f_(struct First_Second_Tuple2List* arg_2);
 
 struct First_ListSecond_ListTuple2 fun_(void* env_, struct First_Second_Tuple2List* arg_);
 
@@ -86,7 +86,7 @@ struct First_Second_Tuple2List {
     struct First_Second_Tuple2List* tail;
 };
 
-struct First_ListSecond_ListTuple2 f_(struct First_Second_Tuple2List* __2) {
+struct First_ListSecond_ListTuple2 f_(struct First_Second_Tuple2List* arg_2) {
     struct First_ListSecond_ListTuple2 tuple_;
     tuple_.t0 = NULL;
     tuple_.t1 = NULL;

boot/tests/functions/str_esc/str_esc.c

@@ -1,16 +1,16 @@
 #include "milone.h"
 
-int f_(char __);
+int f_(char arg_);
 
-int g_(struct String __1);
+int g_(struct String arg_1);
 
 int main();
 
-int f_(char __) {
+int f_(char arg_) {
     return 0;
 }
 
-int g_(struct String __1) {
+int g_(struct String arg_1) {
     return 0;
 }