module Maude.Meta.Qid (

Qid,

QidList,

QidSet,

qid,

fromString,

toString

) where

import qualified Common.Id as Id

import qualified Data.Char as Char

import Data.Set (Set)

-- A Quoted Identifier

newtype Qid = Qid { qid :: Id.Id }

deriving (Show, Eq, Ord)

type QidList = [Qid]

type QidSet = Set Qid

-- Convert a Qid to a String.

toString :: Qid -> String

--string (Qid q) = q

toString = show . qid

-- Convert a String to a Qid.

fromString :: String -> Qid

fromString = Qid . Id.stringToId . translate

--- Helper functions for translating a String to a Qid.

-- Quote the identifier by prepending a tick.

-- Don't keep backticks at the beginning of a string.

tick :: String -> String

tick ('`':str) = tick str

tick str = ('\'':str)

-- Escape a special character by prepending a backtick.

-- Don't place backticks at the end of a string.

backtick :: String -> String

backtick "" = ""

backtick str = ('`':str)

-- Translate the string to an identifier by masking all special characters.

translate :: String -> String

translate = tick . foldr escape ""

-- Escape a whitespace or special character.

escape :: Char -> String -> String

escape char str

| isSpecial char = collapse $ backtick (char:str)

| isSpace char = collapse $ backtick str

| otherwise = char:str

where

isSpecial ch = elem ch [ '(', ')', '[', ']', '{', '}', ',' ]

isSpace ch = Char.isSpace ch || ch == '`'

-- Sequences of backticks are collapsed into one.

collapse :: String -> String

collapse ('`':'`':str) = '`':str

collapse str = str