type synonyms

[abau]

Support type synonyms, so we can write:

type Foo = Bar
data Spam = Spam Foo

Possible implementation: expand type synonyms in Template Haskell frontend.

[jwaldmann]

Yes. that would be convenient for writing (documenting) constraint programs.

Implementation should be easy (and needs no expansion)?

• ignore type synonyms when generating code (you do type inference anyway)
• copy the type synonym declarations verbatim (for the "original" code that is used for testing at the end)

[abau]

you do type inference anyway

But type inference fails with type synonyms.

data Bool = False | True
type Foo   = Bool
data Maybe = Just Foo | Nothing
main x = case x of
  Just b     -> b
  Nothing -> False

gives

No unifier found for 'Foo' and 'Bool'

Anyway, I implemented synonym expansion in TH frontend (cf. 60c8dba). It's supposed to work with both non-parametrized synonyms

type Foo = ....

and parametrized synonyms

type Foo x = ... x ....