Data.OpenADT.TH

This module exports template haskell functions for generating tedious boilerplate.

Documentation

mkVarPattern

Arguments

:: Name

The Name of the type to create patterns for.

-> String

The label in the variant the constructor will have.

-> String

The name of the fixed pattern.

-> String

The name of the unfixed pattern.

-> Q [Dec]

Create patterns for a variant constructor.

For example, for the type FooF with the constructor FooF':

data FooF a x = FooF' a x
$(mkVarPattern ''FooF "foo" "Foo" "FooF")

A pattern similar to the following will be generated:

pattern FooF :: (OpenAlg r "foo" (FooF a) v) => a -> v -> VarF r v
pattern FooF a v <- VarF (view (Label :: Label "foo") -> Just (FooF' a v))

pattern Foo :: (OpenAlg r "foo" (FooF a) (OpenADT r))
            => a -> OpenADT r -> OpenADT r
  where FooF a v = VarF (IsJust (Label :: Label "foo") (FooF' a v))
pattern Foo  a v = Fix (FooF a v)