From c6bc1e0de579ea9cff446a707ba15182735c4526 Mon Sep 17 00:00:00 2001
From: Christoph Hegemann <christoph.hegemann@dfinity.org>
Date: Mon, 27 Oct 2025 09:46:20 +0100
Subject: [PATCH] feat: relaxes grammar to allow un-parenthesized unary
 operator patterns

---
 doc/md/examples/grammar.txt     |  2 +-
 src/mo_frontend/parser.mly      | 14 +++++++-------
 test/run/ok/pat-subtyping.tc.ok |  2 +-
 test/run/pat-subtyping.mo       |  2 +-
 test/run/switch.mo              |  8 ++++----
 5 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/doc/md/examples/grammar.txt b/doc/md/examples/grammar.txt
index 27736fcc8d9..33a367f4934 100644
--- a/doc/md/examples/grammar.txt
+++ b/doc/md/examples/grammar.txt
@@ -309,6 +309,7 @@
     '_'
     <id>
     <lit>
+    <unop> <lit>
     '(' <list(<pat_bin>, ',')> ')'
 
 <pat_nullary> ::= 
@@ -320,7 +321,6 @@
     '#' <id>
     '#' <id> <pat_nullary>
     '?' <pat_un>
-    <unop> <lit>
 
 <pat_bin> ::= 
     <pat_un>
diff --git a/src/mo_frontend/parser.mly b/src/mo_frontend/parser.mly
index 6d203254512..499f7e82d46 100644
--- a/src/mo_frontend/parser.mly
+++ b/src/mo_frontend/parser.mly
@@ -891,6 +891,13 @@ pat_plain :
     { VarP(x) @! at $sloc }
   | l=lit
     { LitP(ref l) @! at $sloc }
+  | op=unop l=lit
+    { match op, l with
+      | (PosOp | NegOp), PreLit (s, (Type.(Nat | Float) as typ)) ->
+        let signed = match op with NegOp -> "-" ^ s | _ -> "+" ^ s in
+        LitP(ref (PreLit (signed, Type.(if typ = Nat then Int else typ)))) @! at $sloc
+      | _ -> SignP(op, ref l) @! at $sloc
+    }
   | LPAR ps=seplist(pat_bin, COMMA) RPAR
     { (match ps with [p] -> ParP(p) | _ -> TupP(ps)) @! at $sloc }
 
@@ -909,13 +916,6 @@ pat_un :
     { TagP(x, p) @! at $sloc }
   | QUEST p=pat_un
     { OptP(p) @! at $sloc }
-  | op=unop l=lit
-    { match op, l with
-      | (PosOp | NegOp), PreLit (s, (Type.(Nat | Float) as typ)) ->
-        let signed = match op with NegOp -> "-" ^ s | _ -> "+" ^ s in
-        LitP(ref (PreLit (signed, Type.(if typ = Nat then Int else typ)))) @! at $sloc
-      | _ -> SignP(op, ref l) @! at $sloc
-    }
 
 pat_bin :
   | p=pat_un
diff --git a/test/run/ok/pat-subtyping.tc.ok b/test/run/ok/pat-subtyping.tc.ok
index ee6436c0bd3..82b14385aad 100644
--- a/test/run/ok/pat-subtyping.tc.ok
+++ b/test/run/ok/pat-subtyping.tc.ok
@@ -1,5 +1,5 @@
 pat-subtyping.mo:6.8-6.9: warning [M0146], this pattern is never matched
-pat-subtyping.mo:7.8-7.12: warning [M0146], this pattern is never matched
+pat-subtyping.mo:7.8-7.10: warning [M0146], this pattern is never matched
 pat-subtyping.mo:10.8-10.17: warning [M0146], this pattern is never matched
 pat-subtyping.mo:11.8-11.17: warning [M0146], this pattern is never matched
 pat-subtyping.mo:18.8-18.25: warning [M0146], this pattern is never matched
diff --git a/test/run/pat-subtyping.mo b/test/run/pat-subtyping.mo
index dc6fb56345b..4c9a7fd2937 100644
--- a/test/run/pat-subtyping.mo
+++ b/test/run/pat-subtyping.mo
@@ -4,7 +4,7 @@ if false {
 
 switch (magic ()) {
   case 1 {};  // redundant
-  case (-1) {};  // redundant
+  case -1 {};  // redundant
 };
 switch (magic ()) {
   case (1 : Nat) {};  // redundant
diff --git a/test/run/switch.mo b/test/run/switch.mo
index 057ff370079..d12cb2fa4dd 100644
--- a/test/run/switch.mo
+++ b/test/run/switch.mo
@@ -6,10 +6,10 @@ let x1 = switch 2 {
 assert (x1 == 1);
 
 let x2 : Int = switch (-3) {
-  case (0) 0;
-  case (-1) 2;
-  case (-3) 1;
-  case (x) x;
+  case 0 0;
+  case -1 2;
+  case -3 1;
+  case x x;
 };
 assert (x2 == 1);