Haskell Programming Assignment Help by Haskell Expert

				
					module Main
where

import System.IO
import Data.List
import Data.List.Split
import Text.Regex.Posix ((=~))

unify left right = "VALID PATTERN: Left: " ++ left ++ " Right: " ++ right

strip::String -> String
strip x = unwords(words x)

isList::String -> Bool
isList x = do
-- let n = addType "List"
((last x) == ']') && (isType (strip (init x)))

isArg::String -> Bool
isArg x = do
-- let n = addType "Arglist"
let params = splitOn "," x
foldl1' (&&) (map (isType.strip) params)

isFunc::String -> Bool
isFunc x = do
-- let n = addType "Function"
let params = splitOn ") -> " x
if (length params) == 2
then do
let leftStr = strip (params!!0)
let rightStr = strip (params!!1)
if leftStr == []
then isType rightStr
else (isArg leftStr) && (isType rightStr)
else False

isPrimitive::String -> Bool
isPrimitive x = x `elem` ["int", "real", "str"]
-- let n = addType "Primitive"
-- x `elem` ["int", "real", "str"]

isVar::String -> Bool
isVar x = x =~ "[a-zA-Z][a-zA-Z0-9]*"
-- let n = addType "Variable"
-- x =~ "[a-zA-Z][a-zA-Z0-9]*"

isType::String -> Bool
isType [] = False
isType x@('`':y) = isVar y
isType x@('[':y) = isList (strip y)
isType ('(':x) = isFunc x
isType x = isPrimitive x

validate::String -> String
validate x = do
let params = splitOn "&" x
if (length params) == 2
then do
let leftStr = strip (params!!0)
let rightStr = strip (params!!1)
let leftGood = isType leftStr
-- let n = addType "&"
let rightGood = isType rightStr
if leftGood && rightGood
then unify leftStr rightStr
else "ERR"
else "ERR"

main = do
-- putStrLn "Enter a string: "
input <- getLine
let str = strip(input)
if str == "QUIT"
then return ()
else do
let res = validate str
putStrLn res
if res =="ERR" || res == "BOTTOM"
then return ()
else main
in