funpat: A generalization of pattern matching
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)
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For package maintainers and hackage trustees
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Versions [RSS] | 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 2011-07-01T21:55:23Z |
Distributions | |
Reverse Dependencies | 1 direct, 0 indirect [details] |
Downloads | 1083 total (1 in the last 30 days) |
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Status | Docs uploaded by user Build status unknown [no reports yet] |