From 2609f5dda7e7f2773225441ef75967445dd93225 Mon Sep 17 00:00:00 2001
From: Evan Czaplicki <info@elm-lang.org>
Date: Tue, 23 Jul 2013 17:00:05 +0200
Subject: [PATCH] =?UTF-8?q?Add=20support=20for=20`let=20(=3D=3D>)=20=3D=20?=
 =?UTF-8?q?Lambda=20in=20=E2=80=A6`?=
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---
 changelog.txt                |  1 +
 compiler/Parse/Expression.hs | 29 ++++++++++++++++++-----------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/changelog.txt b/changelog.txt
index 4dcb004..0aafb43 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -16,6 +16,7 @@ Syntax:
 * Record Constructors
 * Record type aliases can be closed on the zeroth column
 * (,,) syntax in types
+* "(+) = " is permitted
 * Unparenthesized if, let, case, and lambda in last
   term of a binary expression
 
diff --git a/compiler/Parse/Expression.hs b/compiler/Parse/Expression.hs
index 13f81b5..5583499 100644
--- a/compiler/Parse/Expression.hs
+++ b/compiler/Parse/Expression.hs
@@ -195,17 +195,24 @@ expr = addLocation (choice [ ifExpr, letExpr, caseExpr ])
     <|> binaryExpr 
     <?> "an expression"
 
-funcDef = try (do p1 <- try Pattern.term ; infics p1 <|> func p1)
-          <|> ((:[]) <$> Pattern.expr)
-          <?> "the definition of a variable (x = ...)"
-    where func p@(PVar v) = (p:) <$> spacePrefix Pattern.term
-          func p          = do try (lookAhead (whitespace >> string "="))
-                               return [p]
-          infics p1 = do
-            o:p <- try (whitespace >> anyOp)
-            p2  <- (whitespace >> Pattern.term)
-            return $ if o == '`' then [ PVar $ takeWhile (/='`') p, p1, p2 ]
-                                 else [ PVar (o:p), p1, p2 ]
+funcDef =
+    choice [ do p1 <- try Pattern.term
+                infics p1 <|> func p1
+           , func =<< (PVar <$> parens symOp)
+           , (:[]) <$> Pattern.expr
+           ] <?> "the definition of a variable (x = ...)"
+    where
+      func pattern =
+          case pattern of
+            PVar v -> (pattern:) <$> spacePrefix Pattern.term
+            _ -> do try (lookAhead (whitespace >> string "="))
+                    return [pattern]
+
+      infics p1 = do
+        o:p <- try (whitespace >> anyOp)
+        p2  <- (whitespace >> Pattern.term)
+        return $ if o == '`' then [ PVar $ takeWhile (/='`') p, p1, p2 ]
+                             else [ PVar (o:p), p1, p2 ]
 
 makeFunction :: [Pattern] -> LExpr t v -> LExpr t v
 makeFunction args body@(L a b _) =