haskell - Program design concerning ADTs -

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i have type

data phase = phaseone            | phasetwo            | phasethree deriving enum

and 5 operations on each phase

  • read
  • write
  • validate
  • evalstatus
  • update

i began trying create type class. problem is, same type. i'd able like

instance myclass phasethree   read = ...

also, need overload return type.

i know type classes aren't want. i'm not sure how want. thought of gadt that's not quite right need able have each instance in separate file.

i'd advice on mechanisms need investigate? have given enough information?

i recommend inverting things bit.

data phase = phase {     read :: string -> foo,     write :: foo -> io (),     validate :: foo -> bool,     evalstatus :: io (),     update :: foo -> foo }  phaseone, phasetwo, phasethree :: phase

(or similar rejiggering of classes explicit records).


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