From 98897ccc44795260735bafc5124e0e14052247f2 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Sun, 10 Mar 2019 12:57:20 +0000
Subject: [PATCH] Extend AST for functions, calls and variables

---
 AST.hs | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/AST.hs b/AST.hs
index 424cfbe..2bea002 100644
--- a/AST.hs
+++ b/AST.hs
@@ -1,21 +1,51 @@
 module AST where
 
+import Data.Char
 import Text.Read
 import Text.ParserCombinators.ReadP hiding ((+++), choice)
 
-data BinOpType = Add | Sub | Mul
+data AST = Function String [String] Expr
+         | Eval Expr
   deriving Show
 data Expr = Num Float
           | BinOp BinOpType Expr Expr
+          | Var String
+          | Call String [Expr]
+  deriving Show
+data BinOpType = Add | Sub | Mul
   deriving Show
 
+instance Read AST where
+  readPrec = parseFunction +++ (Eval <$> readPrec)
+    where parseFunction = lift $ do
+            skipSpaces
+            string "def"
+            skipSpaces
+            name <- munch1 isAlpha
+            params <- between (char '(') (char ')') $
+                      sepBy (munch1 isAlpha) skipSpaces
+            skipSpaces
+            body <- between (char '{') (char '}') $
+                      readS_to_P reads
+            skipSpaces
+            return (Function name params body)
+
 instance Read Expr where
   readPrec = choice [ parseNum
+                    , parseVar
+                    , parseCall
                     , parseBinOp '+' Add
                     , parseBinOp '-' Sub
                     , parseBinOp '*' Mul
                     ]
     where parseNum = Num <$> readPrec
+          parseVar = Var <$> lift (munch1 isAlpha)
+          parseCall = do
+            func <- lift (munch1 isAlpha)
+            params <- lift $ between (char '(') (char ')') $
+                        sepBy (readS_to_P reads)
+                              (skipSpaces >> char ',' >> skipSpaces)
+            return (Call func params)
           parseBinOp c typ = step $ do
             a <- prec 11 readPrec
             lift $ do
-- 
2.30.2