# funpat: A generalization of pattern matching

Versions | 0.1 |
---|---|

Dependencies | base (>=4.2.0.2 && <4.4), mtl (>=2.0.1.0 && <3) [details] |

License | BSD-3-Clause |

Author | Gergely Devai |

Maintainer | deva@inf.elte.hu |

Category | Language |

Uploaded | by GergelyDevai at Fri Jul 1 21:55:23 UTC 2011 |

Distributions | NixOS:0.1 |

Downloads | 526 total (4 in the last 30 days) |

Rating | (no votes yet) [estimated by rule of succession] |

Your Rating | |

Status | Docs uploaded by user Build status unknown [no reports yet] Hackage Matrix CI |

This library provides pattern matching with *restricted function patterns*
(RFPs). An expression is an RFP iff exists an equivalent valid Haskell
pattern. For example `("abc" ++ xs)`

is an RFP, because `('a' : 'b' : 'c' : xs)`

is an equivalent valid Haskell pattern. On the other hand, `(xs ++ "abc")`

is not an RFP. Details are discussed in the paper *Restricted Function Patterns*
presented at *TFP 2011*.

*Example 1.* Here is a function to chop off the prefix `"prefix" of strings`

:

unprefix :: String -> String unprefix s = match s $ do with $ \z -> "prefix" ++ z ~> z with $ \z -> z ~> z

*Example 2.* Let's have a small embedded language:

data Expr = Symbol String | Expr :$ Expr deriving (Eq,Show,Typeable) instance Num Expr where fromInteger n = Symbol $ show n a + b = Symbol "+" :$ a :$ b a * b = Symbol "*" :$ a :$ b ...

In order to allow pattern matching on expressions of type `Expr`

, the
following `Matchable`

instance is needed:

instance Matchable Expr where Symbol s .=. Symbol z = Just [s :=: z] (e :$ f) .=. (g :$ h) = Just [e :=: g, f :=: h] _ .=. _ = Nothing

Now we can pattern match on expressions even if the constructors of
the `Expr`

type were hidden:

transform :: Expr -> Expr transform e = match e $ do with $ \a -> 0 + a ~> a with $ \a b c -> a * (b + c) ~> a * b + a * c with $ \a -> a ~> a

## Modules

[Index]

## Downloads

- funpat-0.1.tar.gz [browse] (Cabal source package)
- Package description (as included in the package)