From 1e8299da4982f7193f3ed5cc54c9996c6f7f1a14 Mon Sep 17 00:00:00 2001
From: Vesa Karvonen <vesa.a.j.k@gmail.com>
Date: Thu, 13 Feb 2020 07:30:46 +0200
Subject: [PATCH] Add `(type _)` as an allowed pattern

Previously a hole, `_`, was not allowed in place of the name of a `(type x)`
pattern.
---
 parser.mly     | 7 +++----
 regression.1ml | 4 ++++
 syntax.ml      | 3 +++
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/parser.mly b/parser.mly
index 1bc417ba..6d205c2b 100644
--- a/parser.mly
+++ b/parser.mly
@@ -381,16 +381,15 @@ bind :
 
 atpat :
   | head
-    { if $1.it = "_" then holeP@@at() else varP($1)@@at() }
+    { headP $1 }
   | LBRACE decon RBRACE
     { strP($2)@@at() }
   | LPAR RPAR
     { strP([])@@at() }
   | LPAR patlist RPAR
     { match $2 with [p] -> p | ps -> tupP(ps)@@at() }
-  | LPAR TYPE name typparamlist RPAR
-    { annotP(varP($3.it@@ati 3)@@ati 3,
-        funT($4, TypT@@ati 2, Pure@@ati 2)@@at())@@at() }
+  | LPAR TYPE head typparamlist RPAR
+    { annotP(headP $3, funT($4, TypT@@ati 2, Pure@@ati 2)@@at())@@at() }
 ;
 apppat :
   | atpat
diff --git a/regression.1ml b/regression.1ml
index 7131a14b..024bbb33 100644
--- a/regression.1ml
+++ b/regression.1ml
@@ -28,6 +28,10 @@ Equivalence: {
 
 ;;
 
+hole_is_allowed_type_pattern (type _ _) = ();
+
+;;
+
 type_error { type_error 101 };
 
 ;;
diff --git a/syntax.ml b/syntax.ml
index 666bd84d..f7434a88 100644
--- a/syntax.ml
+++ b/syntax.ml
@@ -251,6 +251,9 @@ let varP(x) = VarB(x, VarE("$"@@x.at)@@x.at)@@x.at, None
 let holeP : bind * typ option =
   EmptyB@@nowhere_region, None
 
+let headP id =
+  if id.it = "_" then holeP@@id.at else varP(id)@@id.at
+
 let asTopt(to1, to2) =
   match to1, to2 with
   | None, None -> None