Functions not data structures
From HaskellWiki
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| - | + | Sometimes the best way to represent data is using a function. | |
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| + | [[Church encoding]] can be used to represent any [[algebraic data type]] using only functions. | ||
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| + | Another example is the following, not very efficient, implementation of a FiniteMap: | ||
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| + | <haskell> | ||
| + | type FiniteMap key elt = key -> Maybe elt | ||
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| + | emptyFM :: FiniteMap key elt | ||
| + | emptyFM = \k' -> Nothing | ||
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| + | addToFM :: (Eq key) => FiniteMap key elt -> key -> elt -> FiniteMap key elt | ||
| + | addToFM m k v = \k' -> if (k == k') then Just v else m k' | ||
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| + | delFromFM :: (Eq k) => FiniteMap key elt -> key -> FiniteMap key elt | ||
| + | delFromFM m k = \k' -> if (k == k') then Nothing else m k' | ||
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| + | lookupFM :: (Eq k) => FiniteMap key elt -> key -> Maybe elt | ||
| + | lookupFM m k = m k | ||
| + | </haskell> | ||
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| + | [[Runtime compilation]] uses functions not data structures to implement an interpretation layer. | ||
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| + | [[Category:Idioms]] | ||
| + | [[Category:FAQ]] | ||
Current revision
Sometimes the best way to represent data is using a function.
Church encoding can be used to represent any algebraic data type using only functions.
Another example is the following, not very efficient, implementation of a FiniteMap:
type FiniteMap key elt = key -> Maybe elt emptyFM :: FiniteMap key elt emptyFM = \k' -> Nothing addToFM :: (Eq key) => FiniteMap key elt -> key -> elt -> FiniteMap key elt addToFM m k v = \k' -> if (k == k') then Just v else m k' delFromFM :: (Eq k) => FiniteMap key elt -> key -> FiniteMap key elt delFromFM m k = \k' -> if (k == k') then Nothing else m k' lookupFM :: (Eq k) => FiniteMap key elt -> key -> Maybe elt lookupFM m k = m k
Runtime compilation uses functions not data structures to implement an interpretation layer.
Categories: Idioms | FAQ
