#12162: Concatenation of type level symbols missing -------------------------------------+------------------------------------- Reporter: augustss | Owner: phadej Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2632 Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I'm indifferent about what to name `(<>)`, but the fact that someone has objected to it means it might be worth starting a thread on the [https://mail.haskell.org/pipermail/libraries/ libraries mailing list] to figure out the community's opinion. I've heard convincing arguments for both `(<>)` and `(++)`. Or `(+++)`, which is what the [https://github.com/konn/ghc-typelits- symbols/blob/cd812f4cfc2e6816a18283a6a0e9bb2d9ea2905e/src/GHC/TypeLits/Symbols/Internal.hs#L6-L8 ghc-typelits-symbols] GHC plugin library has taken to calling this operation. Or `AppendSymbol`, if we really want to explore all options. If you wish to add tests for this feature, there is a portion of the GHC test suite located in `base` [http://git.haskell.org/ghc.git/tree/HEAD:/libraries/base/tests here]. And you're absolutely correct in observing that the `Symbol` API is quite feature-poor at the moment. OtToMH, there are only three useful operations over `Symbol`s in `base`: * You can check whether two symbols are equal (either through type-level equality or through [http://hackage.haskell.org/package/base-4.9.0.0/docs /GHC-TypeLits.html#v:sameSymbol sameSymbol]). * You can compare two symbols lexicographically with [http://hackage.haskell.org/package/base-4.9.0.0/docs/GHC- TypeLits.html#t:CmpSymbol CmpSymbol]. * You can convert a `KnownSymbol` to a `String` value with [http://hackage.haskell.org/package/base-4.9.0.0/docs/GHC- TypeLits.html#v:symbolVal symbolVal]. And that's about it. While it'd be nice to have promoted lists of `Char`s and just promote all operations over lists, that's much more work, and `Symbol`'s all we've got for now, so we might as well work with it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12162#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler