Add sugar for type params in pats like in binds and decls

For example, previously one could write

    foo (id: 'a => a => a) = ;; ...
    bar ({id: 'a => a => a}) = ;; ...

now one could also write

    foo (id 'a: a => a) = ;; ...
    bar ({id 'a: a => a}) = ;; ...

similarly to what can be written in declarations

    type FUN = {
      id 'a: a => a;
    }

The main motivation for this addition is to make it possible to
copy/cut-and-paste between declarations and patterns.

parser.mly

@@ -110,13 +110,13 @@ paramlist :
   | param paramlist
     { $1::$2 }
 ;
+typparam :
+  | param
+    { typParam $1 }
+;
 typparamlist :
   | paramlist
-    { List.map (fun p ->
-        match p.it with
-        | (b, {it = HoleT; at}, i) -> (b, TypT@@at, i)@@p.at
-        | _ -> p
-      ) $1 }
+    { typParamList $1 }
 ;
 arrow :
   | ARROW
@@ -386,6 +386,8 @@ atpat :
     { strP($2)@@at() }
   | LPAR RPAR
     { strP([])@@at() }
+  | LPAR head typparam typparamlist COLON typ RPAR
+    { annotP(varP($2)@@$2.at, funT($3::$4, $6, Pure@@at())@@at())@@at() }
   | LPAR patlist RPAR
     { match $2 with [p] -> p | ps -> tupP(ps)@@at() }
   | LPAR TYPE head typparamlist RPAR
@@ -429,6 +431,9 @@ atdecon :
     { [($1, annotP($5, $3)@@span[ati 2; ati 5])@@at()] }
   | name COLON typ
     { [($1, annotP(varP($1.it@@ati 1)@@ati 1, $3)@@at())@@at()] }
+  | name typparam typparamlist COLON typ
+    { [($1, annotP(varP($1)@@$1.at,
+        funT($2::$3, $5, Pure@@at())@@at())@@at())@@at()] }
   | TYPE name typparamlist
     { [($2, annotP(varP($2.it@@ati 2)@@ati 2,
         funT($3, TypT@@ati 1, Pure@@ati 1)@@at())@@at())@@at()] }

regression.1ml

@@ -30,6 +30,9 @@ Equivalence: {
 
 hole_is_allowed_type_pattern (type _ _) = ();
 
+typparams_allowed (id 'a: a => a) ({alsoId 'x: x => x}) =
+  alsoId (id 1, id "one", alsoId true);
+
 ;;
 
 type_error { type_error 101 };
@@ -167,7 +170,7 @@ in {
 
 ListN = {
   ...ListN;
-  map 'x 'y (xy: x -> y) = rec (map: 'n => t x n -> t y n) =>
+  map 'x 'y (xy: x -> y) = rec (map 'n: t x n -> t y n) =>
     case (t _) {
       nil = nil;
       (::) x xs = xy x :: map xs;

syntax.ml

@@ -69,6 +69,15 @@ let var s =
 
 let index n = "_" ^ string_of_int n
 
+(* Helpers *)
+
+let typParam param =
+  match param.it with
+  | (b, {it = HoleT; at}, i) -> (b, TypT@@at, i)@@param.at
+  | _ -> param
+
+let typParamList paramList =
+  List.map typParam paramList
 
 (* Sugar *)