Splices returning splices
Hello, I'm attempting to write a quasiquoter with relatively full antiquotation support. In doing so, I've arrived at I think an odd problem: the expression grammar in Language.Haskell.TH.Syntax doesn't seem to include splices. This seems to mean that my antiquotations can't themselves include splices, which is quite limiting. Am I misinterpreting? The type system in Template metaprogramming for Haskell seems to imply no such restriction on the occurrences of splices. (As an additional complication: what I really need to do is return typed splices; my quasiquoter relies on its expected type to determine its behavior. However, this seems like an uninteresting extension of the above problem.) Thanks, /g -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
RE: Splices returning splices
Currently it just isn't supported. Suppose you say f x = [| $(g y) |] ...$(f 3) Does $(f 3) mean run (f 3) returning some code with embedded splices, and then run those, or does it mean (as now) call (f 3), and to do so run (g y) first, to generate some code that is spliced into the code returned by f? A quasiquoter is really a splice. That is [foo| blah |] is the same as $(foo blah). So it might be easier to discuss your question in the context of ordinary splices and quotes. You want foo to return code with a splice, thus: foo input_string = [| ...$(other_fun args) |] But foo is in the Q monad anyway, so why not just run (other_fun args) right there in the quasiquoter? Or perhaps make a tiny example to show what you mean (but not using quasiquotation). Simon | -Original Message- | From: Glasgow-haskell-users [mailto:glasgow-haskell-users- | boun...@haskell.org] On Behalf Of J. Garrett Morris | Sent: 23 March 2015 12:47 | To: GHC users | Subject: Splices returning splices | | Hello, | | I'm attempting to write a quasiquoter with relatively full antiquotation | support. In doing so, I've arrived at I think an odd problem: the | expression grammar in Language.Haskell.TH.Syntax doesn't seem to include | splices. This seems to mean that my antiquotations can't themselves | include splices, which is quite limiting. Am I misinterpreting? The | type system in Template metaprogramming for Haskell seems to imply no | such restriction on the occurrences of splices. | | (As an additional complication: what I really need to do is return typed | splices; my quasiquoter relies on its expected type to determine its | behavior. However, this seems like an uninteresting extension of the | above problem.) | | Thanks, | | /g | | -- | The University of Edinburgh is a charitable body, registered in Scotland, | with registration number SC005336. | | ___ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: Splices returning splices
On Mon, Mar 23, 2015 at 3:43 PM, Simon Peyton Jones simo...@microsoft.com wrote: A quasiquoter is really a splice. That is [foo| blah |] is the same as $(foo blah). So it might be easier to discuss your question in the context of ordinary splices and quotes. You want foo to return code with a splice, thus: foo input_string = [| ...$(other_fun args) |] But foo is in the Q monad anyway, so why not just run (other_fun args) right there in the quasiquoter? Or perhaps make a tiny example to show what you mean (but not using quasiquotation). This may not make any sense, but consider something like this: $$(p a: 1, b: $$(p \x: 2, y: 3\), c: 3) Now, my understanding is that 'p' has a type like 'String - Q (TExp a)', where 'a' is instantiated with the expected type of the resulting expression. But I don't see how to synthesize the expected type for the nested (antiquoted) call to 'p' without implementing my own version of Haskell type inference. I'd like to be able to return a term that includes the antiquoted expression, and then rely on the type checker to properly make the second call to 'p'. /g -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
