GitLab

This is a follow-up of the discussion on haskell-cafe: https://mail.haskell.org/pipermail/haskell-cafe/2021-February/133368.html

I have the following kind of template haskell code:

module Bar where
bar :: String
bar = "whatever"

module Foo where
foo :: String -> Name -> Q [Dec]
foo str name = ...

module FooBar where
import Foo
import Bar
foo bar 'bar

It works great as in foo I can use both bar's Name and bar's value computed at compile time.

But it's unsafe for my purpose because a user could call foo "fakeBarValue" 'bar.

I would like a way to quote both the name and the value of an import into an unforgeable value (by the user, TH can obviously):

module TH.Internal
  ( Named -- constructor not exported
  , namedThing
  , namedName
  )
where
data Named a = Named { namedThing :: a, namedName :: Name }

module Foo where
foo :: Named String -> Q [Dec]
foo n = ...

module FooBar where
import Foo
import Bar
foo '''bar -- new kind of quote?

Or perhaps an alternative way would be to lift the stage restriction ("‘name’ is used in a top-level splice, quasi-quote, or annotation, and must be imported, not defined locally") for imported names? It would allow:

module Foo (foo) where
foo :: ImportedName -> Q [Dec]
foo name = ... $(varE name)...

module FooBar where
import Foo
import Bar
foo 'bar