Test.Extrapolate.Derive

This module is part of Extrapolate, a library for generalization of counter-examples.

This is a module for deriving Generalizable instances.

Needs GHC and Template Haskell (tested on GHC 8.0).

If Extrapolate does not compile under later GHCs, this module is the probable culprit.

Documentation

deriveGeneralizable :: Name -> DecsQ

Derives a Generalizable instance for a given type Name.

Consider the following Stack datatype:

data Stack a = Stack a (Stack a) | Empty

Writing

deriveGeneralizable ''Stack

will automatically derive the following Generalizable instance:

instance Generalizable a => Generalizable (Stack a) where
  expr s@(Stack x y) = constant "Stack" (Stack ->>: s) :$ expr x :$ expr y
  expr s@Empty       = constant "Empty" (Empty   -: s)
  instances s = this "s" s
              $ let Stack x y = Stack undefined undefined `asTypeOf` s
                in instances x
                 . instances y

This function needs the TemplateHaskell extension.

deriveGeneralizableIfNeeded :: Name -> DecsQ

Same as deriveGeneralizable but does not warn when instance already exists (deriveGeneralizable is preferable).

deriveGeneralizableCascading :: Name -> DecsQ

Derives a Generalizable instance for a given type Name cascading derivation of type arguments as well.