#4024: Making toList a member of Foldable
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Reporter: Eelis- | Owner:
Type: proposal | Status: new
Priority: normal | Component: libraries/base
Version: 6.12.1 | Keywords: Foldable, toList
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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The toList function in Data.Foldable is currently not a member of the
Foldable type class, and is consequently not specializable.
This is a great shame, because for data types such as [a] and
data NonEmptyList a = NonEmptyList a [a]
conversion to list can trivially be implemented in O(1) instead of the
generic toList's O(n).
In other words, any code that directly or indirectly uses Foldable's
toList on values of these types needlessly performs O(n) conversions where
O(1) conversions are available.
Fortunately, the solution is very simple: just make toList a member of the
Foldable type class.
I'm attaching a patch that does just this.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4024>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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