Created
March 22, 2017 18:48
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Oswego CSA - Haskell Workshop Code
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module Lib where | |
import Text.Parsec | |
import Text.Parsec.String (Parser) | |
someFunc :: IO () | |
someFunc = putStrLn "someFunc" | |
numberStringParser :: Parser String | |
numberStringParser = many1 digit | |
numberParser :: Parser Int | |
numberParser = fmap read numberStringParser | |
data Operator = Add | Subtract | |
deriving (Show) | |
readOperator :: String -> Operator | |
readOperator "+" = Add | |
readOperator "-" = Subtract | |
readOperator _ = error "Undefined operator" | |
addParser :: Parser String | |
addParser = string "+" | |
subtractParser :: Parser String | |
subtractParser = string "-" | |
operatorStringParser :: Parser String | |
operatorStringParser = addParser <|> subtractParser | |
operatorParser :: Parser Operator | |
operatorParser = fmap readOperator operatorStringParser | |
data Expression = Literal Int | Operation Expression Operator Expression | |
deriving (Show) | |
literalParser :: Parser Expression | |
literalParser = fmap Literal numberParser | |
operationParser :: Parser Expression | |
operationParser = do | |
_ <- string "(" | |
firstExp <- expressionParser | |
operator <- operatorParser | |
secondExp <- expressionParser | |
_ <- string ")" | |
let expression = Operation firstExp operator secondExp | |
return expression | |
expressionParser :: Parser Expression | |
expressionParser = operationParser <|> literalParser | |
performOperation :: Operator -> Int -> Int -> Int | |
performOperation Add a b = a + b | |
performOperation Subtract a b = a - b | |
evaluate :: Expression -> Int | |
evaluate (Literal n) = n | |
evaluate (Operation exp1 op exp2) = performOperation op (evaluate exp1) (evaluate exp2) | |
evaluationParser :: Parser Int | |
evaluationParser = fmap evaluate expressionParser |
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