Cmd.hs

module Calculator.Parser.Cmd (parseCmd) where

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import           Calculator.Parser.Base        (parseId)
import           Calculator.Parser.Expr        (parseExpr)
import           Calculator.Prim.Cmd           (Cmd (..))

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import           Text.ParserCombinators.Parsec

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-- cmd -> ':' cmd'

parseCmd :: Parser Cmd
parseCmd = char ':' >> parseCmd'

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-- cmd' -> reset | assign

parseCmd' :: Parser Cmd
parseCmd' = parseHelp <|> parseReset <|> parseAssign <|> parseFunc

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-- help -> "?" | "help"

parseHelp :: Parser Cmd
parseHelp = (string "?" <|> string "help") >> return Help

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-- reset -> "reset"

parseReset :: Parser Cmd
parseReset = string "reset" >> return Reset

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-- assign -> "var" id "=" expr

parseAssign :: Parser Cmd
parseAssign = do
  _   <- string "var "
  str <- parseId
  _   <- char '='
  ex  <- parseExpr
  return $ Assign str ex

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-- func  -> "func" id arg "=" expr

parseFunc :: Parser Cmd
parseFunc = do
  _   <- string "func "
  str <- parseId
  _   <- char '('
  arg <- parseId
  _   <- char ')'
  _   <- char '='
  ex  <- parseExpr
  return $ Func str arg ex

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