[Haskell-beginners] Question about typeclasses

keke iamkeke at gmail.com
Sat Jan 3 03:17:17 EST 2009


I am bit struggling with understanding the typeclasses usage in
Text.Regex.Posix (=~) while reading Real world haskell.

The type of (=~) is (RegexMaker Regex CompOption ExecOption source,
RegexContext Regex source1 target)  => source1 -> source -> target

I am from Java world. My question is that can I understand source1 in the
way which is a value has type of RegexMaker, Regex, CompOption and

And the definiton of instance RegexMaker Regex CompOption ExecOption
Stringmakes it possible for us to pass a String as the parameter of

Where can I find some good metarials about GHC's type classes? I googled a
lot but can not find something mentioned above usage.

We paranoid love life
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