[racket] meta-languages and going back to the "normal" reader

I think the problem may be in `at-exp`.

If you change 

 pkgs/racket-pkgs/at-exp-lib/at-exp/lang/reader.rkt

and replace the use of `at-readtable` with `(make-at-readtable)`, does
that fix the problem?

At Thu, 10 Jul 2014 11:30:18 -0400, "Alexander D. Knauth" wrote:
> 
> On Jul 10, 2014, at 6:40 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> 
> > The readtable strategy works when <language> itself uses a
> > readtable-based reader. The idea is that you install a mapping for `#λ`
> > while leaving all the other mappings in place. If <language> uses a
> > readtable-based reader, then it picks up your extension, otherwise it
> > doesn't.
> > 
> > I think a `#lang afl at-exp racket` combination should work fine: `afl`
> > installs a handler for `#λ`, `at-exp` installs a handler for `@`, and
> > `racket` uses `read-syntax` to see both extensions.
> 
> Well for some reason it doesn’t:
> #lang afl at-exp racket/base
> (map #λ(+ % 1) '(1 2 3)) ; read: bad syntax `#λ’
> 
> But also for some reason this does:
> #lang at-exp afl racket/base
> (map #λ(+ % 1) '(1 2 3)) ; '(2 3 4)
> (map #λ@+[% 1] ‘(1 2 3)) ; ‘(2 3 4)
> By the way I only just got this to work yesterday by doing basically this but 
> for afl:
> https://github.com/AlexKnauth/rackjure/commit/5fa266e672d529dde227ef216aaef157fa
> 5c618c
> 
> Also is there any way to get something like this to work?:
> #lang afl at-exp racket/base
> @#λ(+ % 1)[1] ; read: bad syntax `#λ'
> 
> > Adding `#fn` support is a little trickier if you want to fall back to
> > `#f` or `#false` when the character after `#f` (as determined by a
> > peek) is not `n`. For that case, the readtable addition for `#f` should
> > remember the old readtable, and then when it needs to fall back, it
> > calls `read/recursive` with the saved readtable as the third argument.
> > That way, immediate parsing of `#f...` uses the saved readtable without
> > `afl` extensions, while parsing of sub-expressions will return to the
> > current readtable that includes the `afl` extensions.
> 
> Do you mean like this?:
> (define lambda-readtable (current-readtable))
> (parameterize ([current-readtable orig-readtable])
>   (read-syntax/recursive src in #f lambda-readtable))
> 
> > Documentation for the functions from a "<language>/lang/reader.rkt" is
> > in section 1.3.18 of the Reference, which defines `#lang` (as being
> > "like `#reader`, which is described in the same section).
> 
> Ok I just found this in section 1.3.18:
> The arity of the resulting procedure determines whether it accepts extra 
> source-location information: a read procedure accepts either one argument (an 
> input port) or five, and aread-syntax procedure accepts either two arguments (a 
> name value and an input port) or six. In either case, the four optional 
> arguments are the reader’s module path (as a syntax object in read-syntax mode) 
> followed by the line (positive exact integer or #f), column (non-negative exact 
> integer or #f), and position (positive exact integer or #f) of the start of the 
> #reader form. 
> 
> But maybe there should be a link or something to section 1.3.18 from sections 
> 17.2 and 17.3.1 of the Guide.  
> That would make it a lot easier to find it.  
> 
> > 
> > At Sat, 5 Jul 2014 13:33:27 -0400, "Alexander D. Knauth" wrote:
> >> 
> >> If I have a meta-language like this:
> >> #lang my-meta-lang <language>
> >> And my-meta-lang is similar to at-exp in that it can accept any arbitrary 
> >> language with any arbitrary reader
> >> (as long as it looks at the readtable), then how do I escape back to the 
> reader 
> >> specified by <language>
> >> from inside a reader macro from my-meta-lang?
> >> 
> >> What I’m trying to do is something like #lang afl <language> where afl adds 
> >> rackjure-like anonymous function literals
> >> to <language>.  
> >> 
> >> So to parse this:
> >> #lang afl racket
> >> #λ(+ % 1)
> >> It would use the racket reader but wrap it to use the afl-readtable, which 
> >> includes dispatch-macros that would
> >> read the (+ % 1) and parse the result into a lambda expression.  
> >> 
> >> But if <language> was something else, with a different reader, then how 
> could I 
> >> use that to read the (+ %1 1).
> >> 
> >> For example if it was something like this:
> >> #lang afl at-exp racket
> >> #λ@+[% 1]
> >> 
> >> There’s also another problem.  If it was this:
> >> #lang afl <language>
> >> #f
> >> Or this:
> >> #lang afl <language>
> >> #false
> >> Or some other thing starting with f that means something to <language>,
> >> Then it would see the #f and hope that it would turn out to be #fn.  If it 
> >> doesn’t, then it uses the racket reader
> >> (instead of the one provided by <language>) to read the #f or the #false.  
> >> 
> >> So back to my original question: How do I escape back to the reader 
> specified 
> >> by <language>
> >> from inside a reader macro?  
> >> 
> >> By the way I can’t find anything in the docs about what the arguments to the 
> >> read and read-syntax functions
> >> provided by <language>/lang/reader.rkt are supposed to be or mean.  
> >> 
> >> 
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