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ghci list typeclasses that a type is in

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  ghci list typeclasses that a type is in Jim Burton <j.burton@brighton.ac.uk> - 2014-10-24 12:27 +0100
    Re: ghci list typeclasses that a type is in Mark Carroll <mtbc@bcs.org> - 2014-10-24 12:53 +0100

#298 — ghci list typeclasses that a type is in

Hi, is it possible to use ghci to list all typeclasses that some type is
an instance of? E.g. I can use :info Eq to see all instances of Eq, but
I want to do it the other way round, e.g. :info String...

TIA,

Jim

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#299

Jim Burton <j.burton@brighton.ac.uk> writes:

> Hi, is it possible to use ghci to list all typeclasses that some type is
> an instance of? E.g. I can use :info Eq to see all instances of Eq, but
> I want to do it the other way round, e.g. :info String...

It will usually work the other way around: your problem with String is
that it isn't a type in its own right, it's just an alias for a list of
Char:

Prelude> :info Char
data Char = GHC.Types.C# GHC.Prim.Char#         -- Defined in
`GHC.Types'
instance Bounded Char -- Defined in `GHC.Enum'
instance Enum Char -- Defined in `GHC.Enum'
instance Eq Char -- Defined in `GHC.Classes'
instance Ord Char -- Defined in `GHC.Classes'
instance Read Char -- Defined in `GHC.Read'
instance Show Char -- Defined in `GHC.Show'
Prelude> ['a','b','c']
"abc"

-- Mark

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