[GHC] #13608: Expose the type of quasiquotes

[GHC]

#13608: Expose the type of quasiquotes
-------------------------------------+-------------------------------------
        Reporter:                    |                Owner:
  facundo.dominguez                  |  facundo.dominguez
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  QuasiQuotes
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  12778             |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by facundo.dominguez):

 > What does parseExp do?

 In the case of the `java` quasiquoter:
 * it adds a finalizer which generates the java method to call, e.g.
 `Object fresh_name() { return  0.0; }`
 * it inserts at the quasiquote location some foreign calls to have the
 generated java method invoked, and the result marshaled to Haskell.

 > What if the type mentions in-scope type variables (existentially or
 lambda bound)?

 In that case, the variables will likely show up in the type returned by
 `reify`. We don't care much about that case, as the user of inline-java
 would be asked to add enough of a type signature to provide as much
 information as necessary to infer a reasonable type in java.

 Also, if you want to explore it, there would be an alternative design
 where it is possible to avoid introducing the variable
 `__ghc_qq_<hash_loc>`. This would involve extending the `Quasi` monad with
 a method
 {{{
 qTypeOfCurrentQuasiQuote :: m TH.Type
 }}}
 which must be invoked in a module finalizer and yields the type of the
 quasiquote, which would require some interaction with the typechecker.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13608#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler