No Typeable instance for type-level literals and promoted types

There's no Typeable instance for string and numeric literals. E.g.

Prelude GHC.TypeLits Data.Typeable> typeRep (Proxy :: Proxy "foo")

<interactive>:15:1:
    No instance for (Typeable "foo") arising from a use of ‘typeRep’
    In the expression: typeRep (Proxy :: Proxy "foo")
    In an equation for ‘it’: it = typeRep (Proxy :: Proxy "foo")

This means that we can't have a Typeable instance for phantom types parameterised by these literals.

Ditto for the promoted data types:

Prelude Data.Typeable> typeRep (Proxy :: Proxy Nothing)

<interactive>:4:1:
    No instance for (Typeable 'Nothing) arising from a use of ‘typeRep’
    In the expression: typeRep (Proxy :: Proxy Nothing)
    In an equation for ‘it’: it = typeRep (Proxy :: Proxy Nothing)

changed weight to 5

added Tbug Trac import labels

closed

In commit 0354fb36:

Author: Iavor S. Diatchki <>
Date:   Sat Jun 14 14:08:23 2014 -0700

    Implement `Typeable` support for type-level literals (#8778).

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
Related	→ #8778 (closed)

changed title from No Typeable instance for type-level literals to No Typeable instance for type-level literals and promoted types

changed the description

Thanks thomie. Is the second part fixed as well?

Yes, it will be in 7.10:

Prelude Data.Typeable> typeRep (Proxy :: Proxy Nothing)
Nothing

added Pnormal label