From ff7fe0a1d35616722cf4dba7ccf4d242582c726c Mon Sep 17 00:00:00 2001
From: sudoer777 <git@sudoer.ch>
Date: Thu, 7 Sep 2023 22:57:12 -0500
Subject: [PATCH] Create very basic equation parser

---
 README.md                            | 15 +++++---
 app/Main.hs                          | 51 ++++++++++++++++++++++++++--
 really-bad-compiler-in-haskell.cabal |  5 ++-
 3 files changed, 64 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index f80b32f..55dc53d 100644
--- a/README.md
+++ b/README.md
@@ -6,17 +6,24 @@ Main repo: https://git.sudoer.ch/me/really-bad-compiler-in-haskell
 
 ## Build Instructions
 
-Clone the repo. Then, use `ghcup tui` to install all of the Haskell tools.
+- Clone the repo.
+- Use `ghcup` to install all of the Haskell tools.
+- Use `stack build` and `stack run <file>` to run the program.
 
 ## Credits
 
-### Learning Resources
+### Learning Resources Used
 
 - Introduction to Compiler Design class at The University of Texas at Dallas, taught by Charles Averill
+- learnyouahaskell.com (for learning Haskell basics)
+- https://akashagrawal.me/2017/01/19/beginners-guide-to-megaparsec.html
+- https://markkarpov.com/tutorial/megaparsec.html (for help writing a Haskell equation parser)
 
 ### Tools
 
 - Language: Haskell
-- Language-specific tools: GHCup, Stack, Cabal
+- Haskell tools: GHCup, Stack, Cabal
+- Libraries: megaparsec, parser-combinators, text
 - IDE: VSCodium
-- Git tool: Forgejo
+- Git platform: Forgejo
+- AI: Phind
diff --git a/app/Main.hs b/app/Main.hs
index 65ae4a0..e6f83b1 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,4 +1,51 @@
-module Main where
+module Main (main) where
+
+import Control.Monad.Combinators.Expr
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char as C
+import Text.Megaparsec.Char.Lexer as L
+
+type Parser = Parsec Void String
+
+data Expr
+  = Int Int
+  | Add Expr Expr
+  | Sub Expr Expr
+  | Mul Expr Expr
+  | Div Expr Expr
+  deriving (Show)
+
+lexemeParser :: Parser a -> Parser a
+lexemeParser = L.lexeme C.space
+
+symbolParser :: String -> Parser String
+symbolParser = L.symbol C.space
+
+intParser :: Parser Int
+intParser = lexemeParser L.decimal
+
+term :: Parser Expr
+term = Int <$> intParser
+
+table :: [[Operator Parser Expr]]
+table =
+  [ [ binaryOp "*" Mul,
+      binaryOp "/" Div
+    ],
+    [ binaryOp "+" Add,
+      binaryOp "-" Sub
+    ]
+  ]
+
+binaryOp name f = InfixL (f <$ symbolParser name)
+
+expr :: Parser Expr
+expr = makeExprParser term table
+
+parseExpr :: String -> Either (ParseErrorBundle String Void) Expr
+parseExpr = parse (C.space *> expr <* eof) ""
 
 main :: IO ()
-main = putStrLn "Hello, Haskell!"
+main = do
+  print $ parseExpr "2+3* 4"
\ No newline at end of file
diff --git a/really-bad-compiler-in-haskell.cabal b/really-bad-compiler-in-haskell.cabal
index 76a6597..5433bd0 100644
--- a/really-bad-compiler-in-haskell.cabal
+++ b/really-bad-compiler-in-haskell.cabal
@@ -31,6 +31,9 @@ executable really-bad-compiler-in-haskell
 
     -- LANGUAGE extensions used by modules in this package.
     -- other-extensions:
-    build-depends:    base ^>=4.16.4.0,megaparsec
+    build-depends:    base ^>=4.16.4.0
+                    , megaparsec >= 9.2.2
+                    , parser-combinators
+                    , text
     hs-source-dirs:   app
     default-language: Haskell2010