[GHC] #13608: Expose the type of quasiquotes

#13608: Expose the type of quasiquotes -------------------------------------+------------------------------------- Reporter: | Owner: (none) facundo.dominguez | Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1 Haskell | Keywords: QuasiQuotes | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: 12778 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It happens with inline-java that {{{ [java| 0.0 |] }}} produces a static method in java {{{ Object fresh_name() { return 0.0; } }}} where {{{ double fresh_name() { return 0.0; } }}} would be preferred. This is better because the user would get an error if the expression does not match the expected result type. Examining the context in which the quasiquote is used would allow to build the later variant. However, GHC provides no way to grab the type that it expects of the quasiquote. The quasiquote desugars as follows: {{{ [java| 0.0 |] ====> $(parseExp java " 0.0 ") }}} We have experimented with a patch that desugars instead like {{{ [java| 0.0 |] ====> let __ghc_qq_ = $(parseExp java " 0.0 ") in __ghc_qq_ }}} The quasiquoter can learn then of the expected type by doing: {{{ do qqName <- getCurrentQuasiQuoteName addModFinalizer $ reify qqName >>= ... where getCurrentQuasiQuoteName :: Q Name getCurrentQuasiQuoteName = do loc <- TH.location return $ mkName $ "__ghc_qq_" ++ hash loc }}} Where `getCurrentQuasiQuoteName` can be provided in `Language.Haskell.TH.Quote`. This addresses the same concern that I initially intended to solve with the more complex proposal in #12778. I hope to submit a patch this week, but it would be useful if people want to provide some feedback about the proposal meanwhile. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13608 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler