Haskell中的正则表达式-了解多参数类型类签名

Question

I'm having hard time figuring out how to use Text.Regex package. What does signature below mean?

class RegexOptions regex compOpt execOpt 
  | regex->compOpt execOpt, compOpt->regex execOpt, execOpt->regex compOpt

I understand that there are three type parameters to RegexOptions and that for each of them, the other two allow compiler to determine its type, but how? What are types or constraints on regex compOpt and execOpt ?

Side question. What would be the type of this expression?

makeRegexOpts (defaultCompOpt { caseSensitive = False }) defaultExecOpt

Answer 1

and that for each of them, the other two allow compiler to determine its type

Not quite. Each of them can be used to deduce the other two , that's what this fundep says.

How this works? Well, magic ! No. The compiler will only allow you to declare one single instance with any particular type appearing at one of the arguments. Then, when it needs a RegexOptions instance and has already deduced any one of the type arguments, it can just look that instance up to obtain the other parameters.