Add control flow

[kaleidoscope-hs.git] / AST.hs

diff --git a/AST.hs b/AST.hs
index 9ff555a74d10c6d970fc8b7df0a37c1d98fdbffc..b019a2a2078f91c18a5046f63e10676f2c40d5aa 100644 (file)
--- a/AST.hs
+++ b/AST.hs
@@ -2,12 +2,14 @@ module AST where
 
 import Data.Char
 import Text.Read 
-import Text.ParserCombinators.ReadP hiding ((+++), choice)
+import Text.ParserCombinators.ReadP hiding ((+++), (<++), choice)
 
 data Expr = Num Double
           | Var String
           | BinOp BinOp Expr Expr
           | Call String [Expr]
+          | If Expr Expr Expr
+          | For String Expr Expr (Maybe Expr) Expr
   deriving Show
 
 data BinOp = Add | Sub | Mul | Cmp Ordering
@@ -17,6 +19,8 @@ instance Read Expr where
   readPrec = parens $ choice [ parseNum
                              , parseVar
                              , parseCall
+                             , parseIf
+                             , parseFor
                              , parseBinOp "<" 10 (Cmp LT)
                              , parseBinOp ">" 10 (Cmp GT)
                              , parseBinOp "==" 10 (Cmp EQ)
@@ -28,10 +32,7 @@ instance Read Expr where
           parseVar = Var <$> lift (munch1 isAlpha)
           parseBinOp s prc op = prec prc $ do
             a <- step readPrec
-            lift $ do
-              skipSpaces
-              string s
-              skipSpaces
+            spaced $ string s
             b <- readPrec
             return (BinOp op a b)
           parseCall = do
@@ -40,6 +41,27 @@ instance Read Expr where
                         sepBy (readS_to_P reads)
                               (skipSpaces >> char ',' >> skipSpaces)
             return (Call func params)
+          parseIf = do
+            spaced $ string "if" 
+            cond <- readPrec
+            spaced $ string "then"
+            thenE <- readPrec
+            spaced $ string "else"
+            elseE <- readPrec
+            return (If cond thenE elseE)
+          parseFor = do
+            spaced $ string "for"
+            identifier <- lift (munch1 isAlpha)
+            spaced $ char '='
+            start <- readPrec
+            spaced $ char ','
+            cond <- readPrec
+            stp <- (spaced (char ',') >> Just <$> step readPrec)
+                     <++ pure Nothing
+            spaced $ string "in"
+            body <- readPrec
+            return (For identifier start cond stp body)
+          spaced f = lift $ skipSpaces >> f >> skipSpaces
             
 data Prototype = Prototype String [String]
   deriving Show