This library provides a "ListT done right implementation" that obeys the Monad laws.

Here is an example of how you build and consume ListT values:

import List.Transformer

import qualified System.IO

stdin :: ListT IO String
stdin = ListT (do
    eof <- System.IO.isEOF
    if eof
        then return Nil
        else do
            string <- getLine
            return (Cons string stdin) )

stdout :: ListT IO String -> IO ()
stdout strings = do
    s <- next strings
    case s of
        Nil                  -> return ()
        Cons string strings' -> do
            putStrLn string
            stdout strings'

main :: IO ()
main = stdout stdin

... and here's an example use of this library to print every natural number using a style resembling list comprehensions:

import List.Transformer

main :: IO ()
main = runListT (do
    n <- select [0..]
    liftIO (print n) )

To learn more, read the tutorial.

Install the stack tool and then run:

$ stack setup
$ stack ghci list-transformer
Prelude> import List.Transformer
Prelude List.Transformer> runListT (do n <- select [0..]; liftIO (print n) )
0
1
2
3
...

This library is pretty small so I don't expect there to be breaking changes since there's not that much that could possibly change.

Copyright (c) 2016 Gabriella Gonzalez All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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