I would like to set the language in the REPL on the fly, with #lang, not using "-I" command-line argument. But this gives me the error "read: #lang not enabled in the current context".
Is there a command-line switch that I'm missing? Or maybe a ",metacommand" I can use? The reason I need this is because I would like to be able to send an Emacs buffer to the Racket REPL, but that won't work if the file starts with #lang.
[Edit]
I can't get C-x C-b to work with #lang either.
But a buffer containing #lang can be sent to a REPL started from Geiser with C-c C-a. This is Switch to REPL and Enter Module from the Geiser drop down menu. If I have a buffer for bugsy.rkt:
;; bugsy.rkt
#lang racket
(define k 6)
(define j 7)
(define (f lhs rhs)
(+ lhs rhs))
Typing C-c C-a gives me this in the REPL:
racket@> ,enter "<filepath>/bugsy.rkt"
[email protected]>
I can then access the module in the REPL:
[email protected]> k
6
[email protected]> (f 3 4)
7
If I want to switch to a different module [or buffer of a file] I can use the ,enter command in the REPL:
[email protected]> ,enter "clyde.rkt"
[email protected]> ,enter "bonny.rkt"
[email protected]>
There is an example of the ,enter command in the documentation. Look above the Dinosaur.
[Original]
According to the Racket documentation #lang has very simple syntax, the reader essentially bootstraps a language syntax from whatever follows the space character after #lang. This means in some sense that #lang is not in Racket's [or any other language's] syntax. Instead it is a implementation feature of the reader which forms part of the larger "Racket" development ecosystem.
Geiser [and presumably Quack and racket-mode] handle this by parsing #lang in elsip before passing code to the Racket REPL. In Geiser, the work is done in geiser-racket.el.
The parsing function is at line 132:
(defun geiser-racket--language ()
(or (cdr (geiser-racket--explicit-module))
(save-excursion
(goto-char (point-min))
(if (re-search-forward "^#lang +\\([^ ]+\\)" nil t)
(geiser-syntax--form-from-string (match-string-no-properties 1))))
"#f"))
And it is called by geiser-racket--geiser-procedure on line 166.
(defun geiser-racket--geiser-procedure (proc &rest args)
(case proc
((eval compile)
(format ",geiser-eval %s %s %s"
(or (car args) "#f")
(geiser-racket--language)
(mapconcat 'identity (cdr args) " ")))
((load-file compile-file)
(format ",geiser-load %S" (geiser-racket--find-module)))
((no-values) ",geiser-no-values")
(t (format ",apply geiser:%s (%s)" proc (mapconcat 'identity args " ")))))
That may give you a starting point for rolling your own code if one of the existing Emacs modes does not meet your needs.