ListT -package:list-transformer

A generator with side-effects.

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The list monad transformer, which extends a monad with non-determinism The type variables signify:

• m - The base monad
• a - The values that the computation yields throughout its execution

For basic construction and composition of ListT computations, much can be accomplished using common typeclass methods.

• return corresponds to yield, yielding a single value.
• (>>=) corresponds to for, calling the second computation once for each time the first computation yields.
• mempty neither yields any values nor produces any effects in the base monad.
• (<>) sequences two computations, yielding all the values of the first followed by all the values of the second.
• lift converts an action in the base monad into a ListT computation which performs the action and yields a single value.

ListT is a newtype wrapper for Producer. You will likely need to use Select and enumerate to convert back and forth between these two types to take advantage of all the Producer-related utilities that Pipes.Prelude has to offer.

• To lift a plain list into a ListT computation, first apply each to turn the list into a Producer. Then apply the Select constructor to convert from Producer to ListT.
• For other ways to construct ListT computations, see the “Producers” section in Pipes.Prelude to build Producers. These can then be converted to ListT using Select.
• To aggregate the values from a ListT computation (for example, to compute the sum of a ListT of numbers), first apply enumerate to obtain a Producer. Then see the “Folds” section in Pipes.Prelude to proceed.

A proper implementation of the list monad-transformer. Useful for streaming of monadic data structures. Since it has instances of MonadPlus and Alternative, you can use general utilities packages like "monadplus" with it.

ListT done right, see https://www.haskell.org/haskellwiki/ListT_done_right_alternative There is also the list-t package on hackage (Nikita Volkov) but it again depends on other packages we do not use yet, so we rather implement the few bits we need afresh.

Lazy monadic computation of a list of results.

A list monad transformer / a monadic list. Monadic list example: A program which reads numbers from the user and accumulates them.

import Control.Monad.ListT.Funcs (repeatM)
import Data.List.Class (execute, scanl, takeWhile, mapL)
import Prelude hiding (scanl, takeWhile)

main =
execute . mapL print .
scanl (+) 0 .
fmap (fst . head) .
takeWhile (not . null) .
fmap reads $ repeatM getLine

Note: The transformers package also has a ListT type, which oddly enough it is not a list monad transformer. This module was deliberately named differently from transformers's module.

Not on Stackage, so not searched. List transformer

Stream the associations passively.

Stream the associations passively.

Stream associations passively.

Stream the elements passively.

This option, when set to True, specifies that we should run in the «list tests» mode.