Add AST and parsing

[kaleidoscope-hs.git] / AST.hs

diff --git a/AST.hs b/AST.hs
new file mode 100644 (file)
index 0000000..b57d7cb
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+++ b/AST.hs
@@ -0,0 +1,65 @@
+module AST where
+
+import Data.Char
+import Text.Read 
+import Text.ParserCombinators.ReadP hiding ((+++), choice)
+
+data Expr = Num Float
+          | Var String
+          | BinOp BinOp Expr Expr
+          | Call String [Expr]
+  deriving Show
+
+data BinOp = Add | Sub | Mul | Cmp Ordering
+  deriving Show
+
+instance Read Expr where
+  readPrec = parens $ choice [ parseNum
+                             , parseVar
+                             , parseCall
+                             , parseBinOp "<" 10 (Cmp LT)
+                             , parseBinOp "+" 20 Add
+                             , parseBinOp "-" 20 Sub
+                             , parseBinOp "*" 40 Mul
+                             ]
+    where parseNum = Num <$> readPrec
+          parseVar = Var <$> lift (munch1 isAlpha)
+          parseBinOp s prc op = prec prc $ do
+            a <- step readPrec
+            lift $ do
+              skipSpaces
+              string s
+              skipSpaces
+            b <- readPrec
+            return (BinOp op a b)
+          parseCall = do
+            func <- lift (munch1 isAlpha)
+            params <- lift $ between (char '(') (char ')') $
+                        sepBy (readS_to_P reads)
+                              (skipSpaces >> char ',' >> skipSpaces)
+            return (Call func params)
+            
+data Prototype = Prototype String [String]
+  deriving Show
+
+instance Read Prototype where
+  readPrec = lift $ do
+    name <- munch1 isAlpha
+    params <- between (char '(') (char ')') $
+                sepBy (munch1 isAlpha) skipSpaces
+    return (Prototype name params)
+
+data AST = Function Prototype Expr
+         | Extern Prototype
+         | TopLevelExpr Expr
+  deriving Show
+
+instance Read AST where
+  readPrec = parseFunction +++ parseExtern +++ parseTopLevel
+    where parseFunction = do
+            lift $ string "def" >> skipSpaces
+            Function <$> readPrec <*> readPrec
+          parseExtern = do
+            lift $ string "extern" >> skipSpaces
+            Extern <$> readPrec
+          parseTopLevel = TopLevelExpr <$> readPrec