frerich / catamorphism Goto Github PK
View Code? Open in Web Editor NEWA package exposing a function for generating catamorphisms.
License: BSD 3-Clause "New" or "Revised" License
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Support for recent versions of GHC?
Hi,
I would love to use this great package, but unfortunately the build fails with GHC 8.0.2, because of the following unsatisfyable constraints:
base >=4.6 && <4.9, template-haskell >=2.8 && <2.11
I suppose similar issues would exist with GHC 8.2.1.
Would it be possible to get an updated version of this package that remedies this issue, i.e. by means of http://hackage.haskell.org/package/th-abstraction?
Best regards,
Peter
Catamorphism generated for rose tree (e.g. Data.Tree.Tree) is incorrect
Given a standard rose tree definition as in
{-# LANGUAGE TemplateHaskell #-}
import Data.Morphism.Cata
data RoseTree a = Node a [RoseTree a]
$(makeCata defaultOptions ''RoseTree)
main = return ()makeCata as of catamorphism 0.5.0.1 generates the following (incorrect!) function:
λ: :t roseTree
roseTree :: (a1 -> [RoseTree a1] -> a0) -> RoseTree a1 -> a0
The actual type of the catamorphism should have been
roseTree :: (a1 -> [a0] -> a0) -> RoseTree a1 -> a0
It appears that makeCata doesn't realize that it could map the catamorphism over the list. In fact, it could probably do that for every type which instantiates Foldable?
Build fails without KindSignatures
Illegal kind signature: ‘ghc-prim-0.5.1.1:GHC.Types.Type’
Perhaps you intended to use KindSignatures
In the type signature for ‘cataProp’
|
40 | $(makeCata defaultOptions { cataName = "cataProp" } ''Proposition)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I'm not sure if this is behaviour that you have observed, but if so, it may be worth adding a word about it in the documentation.
Update to GHC 7.10.1
Build on GHC 7.10.1 fails because of the base bound:
$ cabal install catamorphism
Resolving dependencies...
cabal: Could not resolve dependencies:
trying: catamorphism-0.3.0.0 (user goal)
next goal: base (dependency of catamorphism-0.3.0.0)
rejecting: base-4.8.0.0/installed-901... (conflict: catamorphism => base>=4.6
&& <4.8)
rejecting: base-4.8.0.0, 4.7.0.2, 4.7.0.1, 4.7.0.0, 4.6.0.1, 4.6.0.0, 4.5.1.0,
4.5.0.0, 4.4.1.0, 4.4.0.0, 4.3.1.0, 4.3.0.0, 4.2.0.2, 4.2.0.1, 4.2.0.0,
4.1.0.0, 4.0.0.0, 3.0.3.2, 3.0.3.1 (global constraint requires installed
instance)Code generated for non-regular recursive types does not typecheck
Using catamorphism 0.5.0.1, the following program fails to compile:
{-# LANGUAGE TemplateHaskell #-}
import Data.Morphism.Cata
data List a = Empty | Cons a (List (List a))
$(makeCata defaultOptions ''List)
main = return ()The makeCata invocation generates code yielding the error message
treecata.hs:6:3:
Couldn't match type ‘a1’ with ‘List a1’
‘a1’ is a rigid type variable bound by
the type signature for list :: a -> (a1 -> a -> a) -> List a1 -> a
at treecata.hs:6:3
Expected type: List a1
Actual type: List (List a1)
Relevant bindings include
a_a2p8 :: List (List a1) (bound at treecata.hs:6:3)
a_a2p7 :: a1 (bound at treecata.hs:6:3)
x_a2p6 :: List a1 (bound at treecata.hs:6:3)
c_a2p5 :: a1 -> a -> a (bound at treecata.hs:6:3)
list :: a -> (a1 -> a -> a) -> List a1 -> a
(bound at treecata.hs:6:3)
In the third argument of ‘list’, namely ‘a_a2p8’
In the second argument of ‘c_a2p5’, namely
‘list c_a2p4 c_a2p5 a_a2p8’
Please allow building with GHC 8.4.1 (base-4.11.0.0, template-haskell-2.13.0.0)
The build seems to work fine when the constraints on base and template-haskell are relaxed.
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