On Jul 10, 2014, at 6:40 AM, Matthew Flatt <mfl...@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/5fa266e672d529dde227ef216aaef157fa5c618c 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. >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users
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