On Monday, March 20, 2017 at 7:25:35 PM UTC+1, Matthew Butterick wrote:
> On Mar 20, 2017, at 2:59 AM, Jan Hondebrink <jrhond...@gmail.com> wrote:
>
> Testing top-interaction with expression: (#%top-interaction + 1 2)
> . +: unbound identifier;
> also, no #%app syntax transformer is bound in: +
>
> So when you pass an expression through to the racket/base #%module-begin, it
> can use the racket/base bindings, but if you pass an expression through to
> the racket/base #%top-interaction it cannot. How can you make
> #%top-interaction use the racket/base bindings?
>
>
>
>
> When you start a source file with this line:
>
>
> #lang s-exp "ME-expander.rkt"
>
>
> You are telling Racket to 1) parse the code into expressions using the
> default `s-exp` (aka Racket-style) reader and 2) use "ME-expander.rkt" as the
> expander module.
>
>
> The expander module supplies the initial set of bindings for the code.
> Conversely, if the expander doesn't provide a certain binding, the code can't
> use it, and you get an unbound-identifier error.
>
>
> Even though "ME-expander.rkt" is written with `#lang racket/base`, it does
> not automatically export the bindings from `racket/base`. If that's the
> behavior you want, you need to add this to "ME-expander.rkt":
>
>
> (provide (all-from-out racket/base))
>
>
> Though you have to be a little careful if you plan to override bindings from
> `racket/base` with your own (say, `#%top-interaction` and `#%module-begin`).
> In that case, you can omit those bindings with `except-out`:
>
>
> (provide (except-out (all-from-out racket/base) #%top-interaction
> #%module-begin))
Thanks for the explanation! It turns out that I don't need "ME-expander.rkt" to
export any bindings apart from #%module-begin and #%top-interaction. I
overcomplicated Greg's suggestion to supply my own #%top-interaction by
thinking it needed to pass its result "up the chain" to the racket/base
#%top-interaction. Just as Beautiful Racket taught me to do with #%module-begin.
But for #%top-interaction it is not necessary. In "ME-expander.rkt" the
following works:
#lang racket/base
(require (for-syntax racket/base))
(define-syntax (ME-module-begin stx)
(syntax-case stx ()
[(_ s-expressions ...)
#'(#%module-begin (apply values
(for/list ([expr (list 's-expressions ...)])
(m-eval expr global-environment)))
)]))
(define-syntax (#%top-interaction stx)
#`(m-eval '#,(cdr (syntax-e stx)) global-environment))
(provide (rename-out (ME-module-begin #%module-begin))
#%top-interaction)
(define (m-eval exp env)
(...
---
So let me try and formulate my understanding if this:
when using #lang s-expr "ME-expander.rkt" in a source file:
- The code in the file (DrRacket definition window) is caught by ME-expander's
ME-module-begin which wraps the transformed code in (#%module-begin ...) which
is then evaluated using the bindings from racket/base + the bindings in
ME-expander (although I'm still a bit shady on how *exactly* that works)
- Anything typed in the REPL window is caught by ME-expander's
#%top-interaction which just transforms code without wrapping it in a special
form, which is then evaluated using the bindings from racket/base + the
bindings in ME-expander.
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