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Fwd: Language spec

From: Stephen Scheck
Subject: Fwd: Language spec
Date: Mon, 17 Aug 2020 10:34:23 -0400


I've been experimenting with implementing a language spec for Gash, such that you can use the shell from the Guile REPL:

    scheme@(guile-user)> ,language gash
    Happy hacking with Guile as Shell!  To switch back, type `,L scheme'.
    gash@(guile-user)> find .
    $1 = 0
    gash@(guile-user)> find foo
    find: 'foo': No such file or directory
    $2 = 1

To achieve this as a simple evaluated language is straightforward:

    (define-module (language gash spec)
      #:use-module (gash parser)
      #:use-module (gash eval)
      #:use-module (gash environment)
      #:use-module (system base language)
      #:export (gash))
    (define-language gash
      #:title "Guile as Shell"
      #:reader (lambda (port env) (read-sh port))
      #:evaluator (lambda (x module) (eval-sh x) (get-status))
      #:printer write)

I'm wondering if there would be any interest in including something like this in Gash?

It's also not difficult to naively compile to tree-il, but I think the way I've done it would not be what is wanted, since it really just compiles the *interpreter* `eval-sh` code. Of course, `eval-sh` examines an _expression_ of Gash tokens, producing bits of Scheme code and immediately evaluating them; a proper compiler should replace the Gash token stream with those same Scheme _expression_ sequences without executing them, and pass that to the tree-il compiler. However, that's beyond the scope of my current familiarity with the Gash implementation.

Happy hacking with Guile as Shell!


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