X-Git-Url: https://git.lukelau.me/?p=kaleidoscope-hs.git;a=blobdiff_plain;f=AST.hs;h=c766afc1570140a77690e9f19259a68def0ac967;hp=5628e7c7cd74c8d0f04d5b4e9c908e245e5696f6;hb=45afeea77cd017d2ac37cf330c595c22c90a7f87;hpb=ae80d076cba678169dbddac4a53edd2cb1e091fb

diff --git a/AST.hs b/AST.hs
index 5628e7c..c766afc 100644
--- a/AST.hs
+++ b/AST.hs
@@ -1,23 +1,35 @@
 module AST where
 
 import Text.Read 
-import Text.ParserCombinators.ReadP hiding ((+++))
+import Text.ParserCombinators.ReadP hiding ((+++), choice)
 
 data Expr = Num Float
-          | Add Expr Expr
+          | Var String
+          | BinOp BinOp Expr Expr
+  deriving Show
+
+data BinOp = Add | Sub | Mul | Cmp Ordering
   deriving Show
 
 instance Read Expr where
-  readPrec = parseNum +++ parseAdd
+  readPrec = choice [ parseNum
+                    , parseVar
+                    , parseBinOp "<" 10 (Cmp LT)
+                    , parseBinOp "+" 20 Add
+                    , parseBinOp "-" 20 Sub
+                    , parseBinOp "*" 40 Mul
+                    ]
     where parseNum = Num <$> readPrec
+          parseVar = Var <$> lift (munch1 isAlpha)
           -- use 'prec 1' and 'step' so that parsing 'a'
           -- can only go one step deep, to prevent ininfite
           -- recursion
-          parseAdd = prec 1 $ do
+          parseBinOp s prc op = prec prc $ do
             a <- step readPrec
             lift $ do
               skipSpaces
-              char '+'
+              string s
               skipSpaces
             b <- readPrec
-            return (Add a b)
+            return (BinOp op a b)
+