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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2016 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (guix build bournish)
#:use-module (system base language)
#:use-module (system base compile)
#:use-module (system repl command)
#:use-module (system repl common)
#:use-module (ice-9 rdelim)
#:use-module (ice-9 match)
#:use-module (ice-9 ftw)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-26)
#:export (%bournish-language))
;;; Commentary:
;;;
;;; This is a super minimal Bourne-like shell language for Guile. It is meant
;;; to be used at the REPL as a rescue shell. In a way, this is to Guile what
;;; eshell is to Emacs.
;;;
;;; Code:
(define (expand-variable str)
"Return STR or code to obtain the value of the environment variable STR
refers to."
;; XXX: No support for "${VAR}".
(if (string-prefix? "$" str)
`(or (getenv ,(string-drop str 1)) "")
str))
(define* (display-tabulated lst
#:key (columns 3)
(column-width (/ 78 columns)))
"Display the list of string LST in COLUMNS columns of COLUMN-WIDTH
characters."
(define len (length lst))
(define pad
(if (zero? (modulo len columns))
0
columns))
(define items-per-column
(quotient (+ len pad) columns))
(define items (list->vector lst))
(let loop ((indexes (unfold (cut >= <> columns)
(cut * <> items-per-column)
1+
0)))
(unless (>= (first indexes) items-per-column)
(for-each (lambda (index)
(let ((item (if (< index len)
(vector-ref items index)
"")))
(display (string-pad-right item column-width))))
indexes)
(newline)
(loop (map 1+ indexes)))))
(define ls-command-implementation
;; Run-time support procedure.
(case-lambda
(()
(display-tabulated (scandir ".")))
(files
(let ((files (filter (lambda (file)
(catch 'system-error
(lambda ()
(lstat file))
(lambda args
(let ((errno (system-error-errno args)))
(format (current-error-port) "~a: ~a~%"
file (strerror errno))
#f))))
files)))
(display-tabulated files)))))
(define (ls-command . files)
`((@@ (guix build bournish) ls-command-implementation) ,@files))
(define (which-command program)
`(search-path ((@@ (guix build bournish) executable-path))
,program))
(define (cat-command file)
`(call-with-input-file ,file
(lambda (port)
((@ (guix build utils) dump-port) port (current-output-port))
*unspecified*)))
(define (help-command . _)
(display "\
Hello, this is Bournish, a minimal Bourne-like shell in Guile!
The shell is good enough to navigate the file system and run commands but not
much beyond that. It is meant to be used as a rescue shell in the initial RAM
disk and is probably not very useful apart from that. It has a few built-in
commands such as 'ls' and 'cd'; it lacks globbing, pipes---everything.\n"))
(define %not-colon (char-set-complement (char-set #\:)))
(define (executable-path)
"Return the search path for programs as a list."
(match (getenv "PATH")
(#f '())
(str (string-tokenize str %not-colon))))
(define %commands
;; Built-in commands.
`(("echo" ,(lambda strings `(list ,@strings)))
("cd" ,(lambda (dir) `(chdir ,dir)))
("pwd" ,(lambda () `(getcwd)))
("rm" ,(lambda (file) `(delete-file ,file)))
("cp" ,(lambda (source dest) `(copy-file ,source ,dest)))
("help" ,help-command)
("ls" ,ls-command)
("which" ,which-command)
("cat" ,cat-command)))
(define (read-bournish port env)
"Read a Bournish expression from PORT, and return the corresponding Scheme
code as an sexp."
(match (string-tokenize (read-line port))
((command args ...)
(match (assoc command %commands)
((command proc) ;built-in command
(apply proc (map expand-variable args)))
(#f
(let ((command (if (string-prefix? "\\" command)
(string-drop command 1)
command)))
`(system* ,command ,@(map expand-variable args))))))))
(define %bournish-language
(let ((scheme (lookup-language 'scheme)))
(make-language #:name 'bournish
#:title "Bournish"
#:reader read-bournish
#:compilers (language-compilers scheme)
#:decompilers (language-decompilers scheme)
#:evaluator (language-evaluator scheme)
#:printer (language-printer scheme)
#:make-default-environment
(language-make-default-environment scheme))))
;; XXX: ",L bournish" won't work unless we call our module (language bournish
;; spec), which is kinda annoying, so provide another meta-command.
(define-meta-command ((bournish guix) repl)
"bournish
Switch to the Bournish language."
(let ((current (repl-language repl)))
(format #t "Welcome to ~a, a minimal Bourne-like shell!~%To switch back, type `,L ~a'.\n"
(language-title %bournish-language)
(language-name current))
(current-language %bournish-language)
(set! (repl-language repl) %bournish-language)))
;;; bournish.scm ends here
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