| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Data.HList.HCurry
Description
Convert between functions taking HLists and functions taking many arguments
- class HLengthEq xs n => HCurry' (n :: HNat) f xs r | f xs -> r, r xs -> f, n f -> xs, xs -> n where
- hUncurry :: (ArityRev f n, ArityFwd f n, HCurry' n f xs r) => f -> HList xs -> r
- hCurry :: (ArityRev f n, ArityFwd f n, HCurry' n f xs r) => (HList xs -> r) -> f
- hCompose :: (HSplitAt1 ([] *) n2 xsys xs1 xs2, HCurry' n2 f1 xs1 x, HCurry' n1 b xs2 r, HCurry' n3 f2 xsys r, ArityFwd f1 n2, ArityFwd b n1, ArityRev f1 n2, ArityRev b n1, HAppendList1 * xs1 xs2 xsys) => (x -> b) -> f1 -> f2
- arityOf :: Arity f n => f -> Proxy n
Documentation
class HLengthEq xs n => HCurry' (n :: HNat) f xs r | f xs -> r, r xs -> f, n f -> xs, xs -> n where Source #
'curry'/'uncurry' for many arguments and HLists instead of tuples
XXX the last FD xs -> n is needed to make hCompose infer the right types:
arguably it shouldn't be needed
hCurry :: (ArityRev f n, ArityFwd f n, HCurry' n f xs r) => (HList xs -> r) -> f Source #
Note: with ghc-7.10 the Arity constraint added here does not work
properly with hCompose, so it is possible that other uses of hCurry
are better served by hCurry' Proxy.
hCompose :: (HSplitAt1 ([] *) n2 xsys xs1 xs2, HCurry' n2 f1 xs1 x, HCurry' n1 b xs2 r, HCurry' n3 f2 xsys r, ArityFwd f1 n2, ArityFwd b n1, ArityRev f1 n2, ArityRev b n1, HAppendList1 * xs1 xs2 xsys) => (x -> b) -> f1 -> f2 Source #
compose two functions that take multiple arguments. The result of the second function is the first argument to the first function. An example is probably clearer:
>>>let f = hCompose (,,) (,)>>>:t ff :: ... -> ... -> ... -> ... -> ((..., ...), ..., ...)
>>>f 1 2 3 4((1,2),3,4)
Note: polymorphism can make it confusing as to how many parameters a function
actually takes. For example, the first two ids are id :: (a -> b) -> (a -> b) in
>>>(.) id id id 'y''y'
>>>hCompose id id id 'y''y'
still typechecks, but in that case hCompose i1 i2 i3 x == i1 ((i2 i3) x)
has id with different types than @(.) i1 i2 i3 x == (i1 (i2 i3)) x
Prompted by http://stackoverflow.com/questions/28932054/can-hlistelim-be-composed-with-another-function