/Haskell 8

# Control.Monad.Fix

Copyright (c) Andy Gill 2001, (c) Oregon Graduate Institute of Science and Technology, 2002 BSD-style (see the file libraries/base/LICENSE) libraries@haskell.org experimental portable Trustworthy Haskell2010

#### Description

Monadic fixpoints.

For a detailed discussion, see Levent Erkok's thesis, Value Recursion in Monadic Computations, Oregon Graduate Institute, 2002.

class Monad m => MonadFix m where Source

Monads having fixed points with a 'knot-tying' semantics. Instances of `MonadFix` should satisfy the following laws:

purity
`mfix (return . h) = return (fix h)`
left shrinking (or tightening)
`mfix (\x -> a >>= \y -> f x y) = a >>= \y -> mfix (\x -> f x y)`
sliding
`mfix (liftM h . f) = liftM h (mfix (f . h))`, for strict `h`.
nesting
`mfix (\x -> mfix (\y -> f x y)) = mfix (\x -> f x x)`

This class is used in the translation of the recursive `do` notation supported by GHC and Hugs.

mfix

#### Methods

mfix :: (a -> m a) -> m a Source

The fixed point of a monadic computation. `mfix f` executes the action `f` only once, with the eventual output fed back as the input. Hence `f` should not be strict, for then `mfix f` would diverge.

MonadFix []

#### Methods

mfix :: (a -> [a]) -> [a] Source

MonadFix Maybe

#### Methods

mfix :: (a -> Maybe a) -> Maybe a Source

MonadFix IO

#### Methods

mfix :: (a -> IO a) -> IO a Source

MonadFix Par1

#### Methods

mfix :: (a -> Par1 a) -> Par1 a Source

MonadFix Last

#### Methods

mfix :: (a -> Last a) -> Last a Source

MonadFix First

#### Methods

mfix :: (a -> First a) -> First a Source

MonadFix Product

#### Methods

mfix :: (a -> Product a) -> Product a Source

MonadFix Sum

#### Methods

mfix :: (a -> Sum a) -> Sum a Source

MonadFix Dual

#### Methods

mfix :: (a -> Dual a) -> Dual a Source

MonadFix NonEmpty

#### Methods

mfix :: (a -> NonEmpty a) -> NonEmpty a Source

MonadFix Option

#### Methods

mfix :: (a -> Option a) -> Option a Source

MonadFix Last

#### Methods

mfix :: (a -> Last a) -> Last a Source

MonadFix First

#### Methods

mfix :: (a -> First a) -> First a Source

MonadFix Max

#### Methods

mfix :: (a -> Max a) -> Max a Source

MonadFix Min

#### Methods

mfix :: (a -> Min a) -> Min a Source

MonadFix Identity

#### Methods

mfix :: (a -> Identity a) -> Identity a Source

MonadFix ((->) r)

#### Methods

mfix :: (a -> r -> a) -> r -> a Source

MonadFix (Either e)

#### Methods

mfix :: (a -> Either e a) -> Either e a Source

MonadFix f => MonadFix (Rec1 f)

#### Methods

mfix :: (a -> Rec1 f a) -> Rec1 f a Source

MonadFix (ST s)

#### Methods

mfix :: (a -> ST s a) -> ST s a Source

MonadFix (ST s)

#### Methods

mfix :: (a -> ST s a) -> ST s a Source

(MonadFix f, MonadFix g) => MonadFix ((:*:) f g)

#### Methods

mfix :: (a -> (f :*: g) a) -> (f :*: g) a Source

MonadFix f => MonadFix (Alt * f)

#### Methods

mfix :: (a -> Alt * f a) -> Alt * f a Source

MonadFix f => MonadFix (M1 i c f)

#### Methods

mfix :: (a -> M1 i c f a) -> M1 i c f a Source

(MonadFix f, MonadFix g) => MonadFix (Product * f g)

#### Methods

mfix :: (a -> Product * f g a) -> Product * f g a Source

fix :: (a -> a) -> a Source

`fix f` is the least fixed point of the function `f`, i.e. the least defined `x` such that `f x = x`.

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.0.1/docs/html/libraries/base-4.9.0.0/Control-Monad-Fix.html