From 0503dcb2998ab9dcd0f39e6f264f482a3d2cc7f7 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Sat, 25 Jul 2020 21:51:37 +0200
Subject: Support Let

---
 parser/CC/Parser.hs | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

(limited to 'parser')

diff --git a/parser/CC/Parser.hs b/parser/CC/Parser.hs
index bbabe3c..2d2c4b7 100644
--- a/parser/CC/Parser.hs
+++ b/parser/CC/Parser.hs
@@ -64,7 +64,7 @@ pParenType = do
         _ -> return (TTup tys)
 
 pExpr :: Parser Expr
-pExpr = label (pCall <|> pLam) "expression"
+pExpr = label (pLam <|> pLet <|> pCall) "expression"
   where
     pCall = do
         atoms <- many1 pExprAtom
@@ -90,6 +90,31 @@ pExpr = label (pCall <|> pLam) "expression"
         p2 <- getPosition
         return (Lam (SourceRange p1 p2) names body)
 
+    pLet = do
+        p1 <- try $ do
+            whitespace
+            p <- getPosition
+            void (string "let")
+            return p
+        afterKeyword p1
+      where
+        afterKeyword p1 = do
+            whitespace1
+            lhs <- pName0
+            symbol "="
+            rhs <- pExpr
+            let fullRange rest = mergeRange (SourceRange p1 p1) (range rest)
+            choice [ do p1' <- try $ do
+                            whitespace
+                            p1' <- getPosition
+                            void (string "let")
+                            return p1'
+                        rest <- afterKeyword p1'
+                        return (Let (fullRange rest) lhs rhs rest)
+                   , do symbol "in"
+                        body <- pExpr
+                        return (Let (fullRange body) lhs rhs body) ]
+
 pExprAtom :: Parser Expr
 pExprAtom =
     choice [ uncurry (flip Int) <$> pInt
@@ -119,11 +144,15 @@ pInt = try (whitespace >> pInt0)
 pName0 :: Parser (Name, SourceRange)
 pName0 = do
     p1 <- getPosition
-    c <- pWordFirstChar
-    cs <- many pWordMidChar
+    s <- try $ do
+        c <- pWordFirstChar
+        cs <- many pWordMidChar
+        let s = c : cs
+        guard (s `notElem` ["let", "in"])
+        return s
     p2 <- getPosition
     notFollowedBy pWordMidChar
-    return (c : cs, SourceRange p1 p2)
+    return (s, SourceRange p1 p2)
 
 pWordFirstChar :: Parser Char
 pWordFirstChar = letter <|> oneOf "_$#!"
@@ -146,8 +175,9 @@ token s = try (whitespace >> void (string s))
 emptyLines :: Parser ()
 emptyLines = (try (whitespace >> newline) >> emptyLines) <|> try (whitespace >> eof) <|> return ()
 
-whitespace :: Parser ()
-whitespace = void (many (void (char ' ') <|> void (try (string "\n "))))
+whitespace, whitespace1 :: Parser ()
+whitespace  = void (many  (void (char ' ') <|> void (try (string "\n "))))
+whitespace1 = void (many1 (void (char ' ') <|> void (try (string "\n "))))
 
 getPosition :: Parser SourcePos
 getPosition = do
-- 
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