From 3d32ea6f2146d033b27a28907ad32ca6c7a7279d Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Wed, 5 Jun 2019 22:09:41 +0100
Subject: [PATCH] Parse if expressions

Back to the AST.
---
 AST.hs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/AST.hs b/AST.hs
index 9ff555a..1e505af 100644
--- a/AST.hs
+++ b/AST.hs
@@ -8,6 +8,7 @@ data Expr = Num Double
           | Var String
           | BinOp BinOp Expr Expr
           | Call String [Expr]
+          | If Expr Expr Expr
   deriving Show
 
 data BinOp = Add | Sub | Mul | Cmp Ordering
@@ -17,6 +18,7 @@ instance Read Expr where
   readPrec = parens $ choice [ parseNum
                              , parseVar
                              , parseCall
+                             , parseIf
                              , parseBinOp "<" 10 (Cmp LT)
                              , parseBinOp ">" 10 (Cmp GT)
                              , parseBinOp "==" 10 (Cmp EQ)
@@ -40,6 +42,14 @@ instance Read Expr where
                         sepBy (readS_to_P reads)
                               (skipSpaces >> char ',' >> skipSpaces)
             return (Call func params)
+          parseIf = do
+            lift $ skipSpaces >> string "if" >> skipSpaces
+            cond <- readPrec
+            lift $ skipSpaces >> string "then" >> skipSpaces
+            thenE <- readPrec
+            lift $ skipSpaces >> string "else" >> skipSpaces
+            elseE <- readPrec
+            return (If cond thenE elseE)
             
 data Prototype = Prototype String [String]
   deriving Show
-- 
2.30.2