# Direction of data flow

### From HaskellWiki

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(let vs. where) |
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| monadic composition || <hask> f >>= g </hask> |
| monadic composition || <hask> f >>= g </hask> |
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+ | |- |
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+ | | let expression || <hask> let x = 2 in x*x </hask> || (first definition, then usage) |
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| monadic composition || <hask> g =<< f </hask> |
| monadic composition || <hask> g =<< f </hask> |
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+ | |- |
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+ | | where clause || <hask> x*x where x = 2 </hask> || (first usage, then definition) |
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## Latest revision as of 11:49, 20 March 2007

In Haskell the direction of data flow symbolized by the notations differs amongst the notations. Both directions occur equally frequently:

from left to right:

function definition | f x = x*x |
(input left, output right) |

Lambda | \ x -> x*x | |

do notation | do f; g | |

monadic composition | f >>= g | |

let expression | let x = 2 in x*x |
(first definition, then usage) |

from right to left:

function application | f x f $ x |
(input right, applied function left) |

composition | g . f | |

results of monads | do x <- f | |

monadic composition | g =<< f | |

where clause | x*x where x = 2 |
(first usage, then definition) |

## [edit] 1 Weblinks

- http://www.haskell.org/pipermail/libraries/2005-August/004315.html
- http://www.iba-cg.de/doc/hal1-haskell-with-style.pdf

## [edit] 2 See also

There is still something to translate from De/Flussrichtung