Carl Eastlund
On Wed, Jul 10, 2013 at 11:28 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote: > At Wed, 10 Jul 2013 23:15:46 -0400, Ryan Culpepper wrote: > > On 07/10/2013 09:04 PM, Asumu Takikawa wrote: > > > Hi all, > > > > > > I'm currently trying to fix the Typed Racket unit tests. I think I've > > > narrowed down the issue to a certain syntax property for keyword > > > functions. > > > > > > The issue is illustrated by the following example: > > > > > > #lang racket > > > > > > (require racket/file > > > (for-syntax racket/file > > > racket/keyword-transform)) > > > > > > ;; the property is #f > > > (begin-for-syntax > > > (displayln > > > (syntax-case (expand-syntax #'(copy-directory/files 1 2)) () > > > [(let-values (((temp1) _) > > > ((temp2) _)) > > > (if _ > > > (#%plain-app1 copy-directory/files15 e1 ...) > > > (#%plain-app2 copy-directory/files17 e2 ...))) > > > (syntax-procedure-converted-arguments-property > > #'copy-directory/files15)]))) > > > > > > ;; property is syntax > > > (begin-for-syntax > > > (displayln > > > (syntax-case (local-expand #'(copy-directory/files 1 2) > 'expression > > null) () > > > [(let-values (((temp1) _) > > > ((temp2) _)) > > > (if _ > > > (#%plain-app1 copy-directory/files15 e1 ...) > > > (#%plain-app2 copy-directory/files17 e2 ...))) > > > (syntax-procedure-converted-arguments-property > > #'copy-directory/files15)]))) > > > > > > There are two syntax-time computations here. Both are expanding an > > > application of a keyword function (one with local-expand, one with > > > expand) and looking at the resulting syntax. > > > > > > The key point here is that I want to find the property looked up by > > > `syntax-procedure-converted-arguments-property` on an output identifier > > > because Typed Racket needs it to type-check the expansion. > > > > > > Unfortunately, as the comments indicate, only the second piece of code > > > can find the property. The reason appears to be that the property key > is > > > actually a private `gensym`ed symbol and the two pieces of code appear > > > to get separate instantiations of the kw.rkt module (perhaps at > different > > > phases). > > > > > > To check that, if I modify kw.rkt to use a plain symbol, both of the > > > snippets above return the same property value. > > > > > > Anyone have any idea how I can keep using `expand` but still be able to > > > look up the property? > > > > To get information about a phase-0 '#%app' expansion, you need to call > > the phase-1 version of 'syntax-procedure-converted-arguments-property'. > > That's going to require a bit of phase-crossing trickery, because the > > identifier you want to query is a phase-0 (dynamic) value, and you want > > the result as a phase-0 value, but the phase-1 function naturally > > consumes and produces phase-1 values. > > > > One solution is to use 'quote-syntax', 'eval', and 'phase1-eval' all > > together. Use 'eval' with 'quote-syntax' to convert the phase-0 > > identifier to a phase-1 identifier. Use 'phase1-eval' to run the > > computation at phase 1 and capture the phase-1 result as a phase-0 value > > (also using 'quote-syntax'). > > I haven't thought about this much, but would it make more sense to move > the property key to a cross-phase persistent module (with a `protected' > provide) in this case? > That came up on IRC. I believe Asumu said the key is an uninterned identifier, meaning it's a stateful value. Right now, cross-phase persistent modules can't store anything stateful other than generative struct types. --Carl
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