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POHaskell: composing function with two floating arguments fails
primarykey
Id
4340992
data
AcceptedAnswerId
4341123
AnswerCount
3
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2010-12-02T23:14:31.760
FavoriteCount
2
LastActivityDate
2015-09-02T15:31:57.073
LastEditDate
2015-09-02T15:31:57.073
LastEditorUserId
247623
OwnerUserId
528678
ParentId
0
PostTypeId
1
Score
6
ViewCount
1001
LastEditorDisplayName
text
Body
I am trying to compose a function of type <code>(Floating a) => a -> a -> a</code> with a function of type <code>(Floating a) => a -> a</code> to obtain a function of type <code>(Floating a) => a -> a -> a</code>. I have the following code: <pre><code>test1 :: (Floating a) => a -> a -> a test1 x y = x test2 :: (Floating a) => a -> a test2 x = x testBoth :: (Floating a) => a -> a -> a testBoth = test2 . test1 --testBoth x y = test2 (test1 x y) </code></pre> However, when I compile it in GHCI, I get the following error: <pre><code>/path/test.hs:8:11: Could not deduce (Floating (a -> a)) from the context (Floating a) arising from a use of `test2' at /path/test.hs:8:11-15 Possible fix: add (Floating (a -> a)) to the context of the type signature for `testBoth' or add an instance declaration for (Floating (a -> a)) In the first argument of `(.)', namely `test2' In the expression: test2 . test1 In the definition of `testBoth': testBoth = test2 . test1 Failed, modules loaded: none. </code></pre> Note that the commented-out version of <code>testBoth</code> compiles. The strange thing is that if I remove the <code>(Floating a)</code> constraints from all type signatures or if I change <code>test1</code> to just take <code>x</code> instead of <code>x</code> and <code>y</code>, <code>testBoth</code> compiles. I've searched StackOverflow, Haskell wikis, Google, etc. and not found anything about a restriction on function composition relevant to this particular situation. Does anyone know why this is happening?
Tags
<haskell><function-composition>
Title
Haskell: composing function with two floating arguments fails
singulars
PostAcceptedAnswerId
1. PO
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 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. USErik Allik
UserOwnerUserId
1. USgdj
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1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. PL
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PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
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 PostTypePostTypeId
 PTAnswer
2. PO
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VotesPostIdCreationDate
1. This table or related slice is empty.
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1. This table or related slice is empty.

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