parsing simple expressions

haskell-experiments/haskell-experiments.cabal

@@ -77,7 +77,7 @@ test-suite haskell-exps-test
     main-is:          Main.hs
 
     -- Test dependencies.
-    build-depends:    base, hspec, langfeatures
+    build-depends:    base, hspec, langfeatures, megaparsec
     other-modules:    Test.OlogsSpec,
         Test.SimpleParserSpec
 

haskell-experiments/src/SimpleParser.hs

@@ -16,23 +16,24 @@
 {-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
 
 module SimpleParser
-  ( eval, Expr (..), BinaryOp (..), UnaryOp (..) ) -- literalParser
+  ( eval, Expr (..), BinaryOp (..), UnaryOp (..), parseExpr ) -- literalParser
 where
 import Text.Megaparsec
 import Data.Void (Void)
-import Text.Megaparsec.Byte.Lexer (decimal)
+import Text.Megaparsec.Char.Lexer (decimal)
-import Control.Concurrent (yield)
+import Text.Megaparsec.Char (char)
 
 type Parser = Parsec Void String
 
-data BinaryOp = Add | Subtract | Multiply | Divide
+data BinaryOp = Add | Subtract | Multiply | Divide deriving (Show, Eq)
 
-data UnaryOp = Negate
+data UnaryOp = Negate deriving (Show, Eq)
 
 data Expr =
   BinaryExpr BinaryOp Expr Expr |
   UnaryExpr UnaryOp Expr |
   Literal Int 
+  deriving (Show, Eq)
 
 lookUpBinaryOp :: BinaryOp -> Int -> Int -> Int
 lookUpBinaryOp Add = (+)
@@ -48,22 +49,29 @@ eval (Literal n) = n
 eval (BinaryExpr binOp a b) = lookUpBinaryOp binOp (eval a) (eval b)
 eval (UnaryExpr unaryOp a) =  lookUpUnaryOp unaryOp (eval a)
 
+parseExpr :: Parser Expr
+parseExpr = choice [
+    try parseBinaryExpr,
+    parseLiteral
+    -- bracketedExpParser,
+    -- negatedExp
+  ]
   
--- parseExpr :: Parser Expr
+parseLiteral :: Parser Expr
--- parseExpr = choice [
+parseLiteral = Literal <$> decimal
---     literalParser,
---     expressionParser
---     -- bracketedExpParser,
---     -- negatedExp
---   ]
 
--- literalParser :: Parser Expr
+parseBinaryExpr :: Parser Expr
--- literalParser = Literal <$> decimal
+parseBinaryExpr = do
+  lhs <- parseLiteral <|> parseExpr
+  binOp <- parseOp
+  rhs <- parseLiteral <|> parseExpr
+  pure (BinaryExpr binOp lhs rhs)
 
--- expressionParser :: Parser Expr
+parseOp :: Parser BinaryOp
--- expressionParser = do
+parseOp = choice [
---   parseExpr
+  char '+' >> pure Add,
---   parseOp
+  char '-' >> pure Subtract,
---   parseExpr
+  char '/' >> pure Divide,
+  char '*' >> pure Multiply
+  ]
 
--- parseOp :: Parser Expr

haskell-experiments/test/Test/SimpleParserSpec.hs

@@ -11,7 +11,7 @@
 module Test.SimpleParserSpec where
 
 import Test.Hspec
-
+import Text.Megaparsec
 import SimpleParser
 
 spec :: Spec
@@ -28,6 +28,8 @@ spec = do
         (UnaryExpr Negate (Literal 1)) 
         (BinaryExpr Divide (Literal 7) (Literal 3))
         ) `shouldBe` 1
-
+    it "can parse basic expressions" $ do
+      parse parseExpr "" "2" `shouldBe` Right (Literal 2)
+      parse parseExpr "" "2+3" `shouldBe` Right (BinaryExpr Add (Literal 2) (Literal 3))
 
 

untitled/.gitignore

@@ -1,29 +0,0 @@
-### IntelliJ IDEA ###
-out/
-!**/src/main/**/out/
-!**/src/test/**/out/
-
-### Eclipse ###
-.apt_generated
-.classpath
-.factorypath
-.project
-.settings
-.springBeans
-.sts4-cache
-bin/
-!**/src/main/**/bin/
-!**/src/test/**/bin/
-
-### NetBeans ###
-/nbproject/private/
-/nbbuild/
-/dist/
-/nbdist/
-/.nb-gradle/
-
-### VS Code ###
-.vscode/
-
-### Mac OS ###
-.DS_Store