From: Luke Lau <luke_lau@icloud.com>
Date: Sun, 10 Mar 2019 15:52:06 +0000 (+0000)
Subject: Parse if statements
X-Git-Url: https://git.lukelau.me/?p=kaleidoscope-hs-old.git;a=commitdiff_plain;h=fff481b022d2d5ed24ce3faf686ca783e7860741

Parse if statements
---

diff --git a/AST.hs b/AST.hs
index 1965ae6..7204136 100644
--- a/AST.hs
+++ b/AST.hs
@@ -8,7 +8,7 @@ newtype Program = Program [AST]
   deriving Show
 
 instance Read Program where
-  readPrec = fmap Program $ lift $ sepBy1 (readPrec_to_P readPrec 0) $ do
+  readPrec = fmap Program $ lift $ sepBy1 (readS_to_P reads) $ do
     skipSpaces
     char ';'
     skipSpaces
@@ -20,8 +20,9 @@ data Expr = Num Float
           | BinOp BinOpType Expr Expr
           | Var String
           | Call String [Expr]
+          | If Expr Expr Expr
   deriving Show
-data BinOpType = Add | Sub | Mul
+data BinOpType = Add | Sub | Mul | Cmp Ordering
   deriving Show
 
 instance Read AST where
@@ -41,9 +42,13 @@ instance Read Expr where
   readPrec = choice [ parseNum
                     , parseVar
                     , parseCall
-                    , parseBinOp '+' Add
-                    , parseBinOp '-' Sub
-                    , parseBinOp '*' Mul
+                    , parseIf
+                    , parseBinOp "+" Add
+                    , parseBinOp "-" Sub
+                    , parseBinOp "*" Mul
+                    , parseBinOp ">" (Cmp GT)
+                    , parseBinOp "<" (Cmp LT)
+                    , parseBinOp "==" (Cmp EQ)
                     ]
     where parseNum = Num <$> readPrec
           parseVar = Var <$> lift (munch1 isAlpha)
@@ -53,11 +58,27 @@ instance Read Expr where
                         sepBy (readS_to_P reads)
                               (skipSpaces >> char ',' >> skipSpaces)
             return (Call func params)
-          parseBinOp c typ = step $ do
+          parseBinOp s typ = step $ do
             a <- prec 11 readPrec
             lift $ do
               skipSpaces
-              char c
+              string s
               skipSpaces
             b <- readPrec
             return (BinOp typ a b)
+          parseIf = do
+            lift $ do
+              string "if"
+              skipSpaces
+            cond <- step readPrec
+            lift $ do
+              skipSpaces
+              string "then"
+              skipSpaces
+            thenE <- step readPrec
+            lift $ do
+              skipSpaces
+              string "else"
+              skipSpaces
+            elseE <- step readPrec
+            return (If cond thenE elseE)