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|
;;
;; SCSH process form notation
;;
;; See http://www.scsh.net/docu/html/man-Z-H-3.html#node_chap_2
;;
;; Some minor changes due to Chicken- and R7RS-incompatible identifiers:
;; | was changed to pipe, |+ was changed to pipe+
;;
;; || wasn't changed, but it's really the zero-length symbol
;;
;; BIG FAT WARNING: Don't mix this with threading, or Bad Things will happen
(module scsh-process
((& fit-pipes) (run fit-pipes) (exec-epf fit-pipes)
exec-path)
(import chicken scheme data-structures)
(use posix)
(define-syntax &
(syntax-rules ()
((_ ?epf ...)
(process-fork (lambda ()
(handle-exceptions exn
;; TODO: Figure out how SCSH does this. It shows the error
;; on stderr in the REPL, but then still quits it.
;; If we just invoke current-handler, it'll get a second REPL
(begin (print-error-message exn) (exit 1))
(exec-epf ?epf ...)))))))
(define-syntax run
(syntax-rules ()
((_ ?epf ...)
;; We reorder the values as they make more sense this way for SCSH compat:
;; scsh returns just the exit code, and conveniently we allow MV in single
;; value continuations, which makes it compatible.
(receive (pid normal-exit? exit-status)
(process-wait (& ?epf ...))
(values exit-status normal-exit? pid)))))
(define (maybe-symbol->string s)
(if (symbol? s) (symbol->string s) s))
;; Perhaps this should really be a procedure?
(define-syntax setup-redirection
(syntax-rules (< > << >> = - stdports)
((_ (< ?file-name)) (setup-redirection (< 0 ?file-name)))
((_ (> ?file-name)) (setup-redirection (> 1 ?file-name)))
((_ (<< ?object)) (setup-redirection (<< 0 ?object)))
((_ (>> ?object)) (setup-redirection (>> 1 ?object)))
((_ (< ?fd ?file-name))
(duplicate-fileno (file-open (maybe-symbol->string `?file-name)
open/rdonly)
`?fd))
((_ (> ?fd ?file-name))
(duplicate-fileno (file-open (maybe-symbol->string `?file-name)
(fx+ open/wronly open/creat))
`?fd))
((_ (<< ?fd ?object)) (error "<< currently not implemented"))
((_ (>> ?fd ?object)) (error ">> currently not implemented"))
((_ (= ?fd-from ?fd/port-to))
(let* ((fd/port-to ?fd/port-to) ; Evaluate once
(fd-to (if (port? fd/port-to)
(port->fileno fd/port-to)
fd/port-to)))
(duplicate-fileno ?fd-from fd-to)))
((_ (- ?fd/port))
(let ((o `?fd/port))
(cond
((fixnum? ?fd/port) (file-close o))
((output-port? ?fd/port) (close-output-port o))
((input-port? ?fd/port) (close-input-port o))
(else (error "Can only close i/o-ports and file descriptor numbers" o)))))
((_ stdports)
(begin (setup-redirection (= 0 (current-input-port)))
(setup-redirection (= 1 (current-output-port)))
(setup-redirection (= 2 (current-error-port)))))
((_ ?arg0 ...)
(syntax-error "Invalid redirection pattern: " `?arg0 ...))))
(define (fit-pipes from-fds to-fds progs)
(define (make-pipes) (map (lambda _ (receive (create-pipe))) to-fds))
(when (null? progs) (error "Can't fit a pipeline between zero programs"))
(let ((initial-pairs (make-pipes)))
;; Close sending ends of these pipes; they're unused.
(for-each (lambda (p) (file-close (cadr p))) initial-pairs)
(let lp ((input-pairs initial-pairs)
(progs progs))
(if (null? (cdr progs))
(begin
;; Fit the final input pipes to their respective fds.
(for-each (lambda (to-fd p)
(duplicate-fileno (car p) to-fd)
(file-close (car p)))
to-fds input-pairs)
((car progs)))
;; Subprocess output goes into fds in output-pairs. Their matching
;; input fds are used as input for the next process in the pipeline.
(let ((output-pairs (make-pipes)))
(process-fork (lambda ()
;; Close receiving end in child and set up linkage
;; from the output descriptors to the created pipes.
(for-each (lambda (p from-fds-for-this-p)
(file-close (car p))
(for-each (lambda (from-fd)
(duplicate-fileno (cadr p) from-fd))
from-fds-for-this-p))
output-pairs from-fds)
;; Set up input descriptors
(for-each (lambda (to-fd p)
(duplicate-fileno (car p) to-fd)
(file-close (car p)))
to-fds input-pairs)
((car progs))))
;; Close sending ends of the output pairs in the parent.
(for-each (lambda (op) (file-close (cadr op))) output-pairs)
(lp output-pairs (cdr progs)))))))
;; The most "core" syntax form
(define-syntax exec-epf
;; The nested let-syntaxes exist to let us pre-empt the fallthrough
;; whenever we see one of the recognised special rules so we don't end up
;; with the generic one if we happen to make a small mistake
(syntax-rules (pipe pipe+ begin epf)
((_ (pipe ?pf0 ?pf1 ...))
(exec-epf (pipe+ ((1 2 0)) ?pf0 ?pf1 ...)))
((_ (pipe+ ?args ...))
(let-syntax
((exec-pipe+
(syntax-rules ___ ()
((_ ((?from0 ?from1 ___ ?to) ___) (?prog0 ?arg0 ___) ___)
(fit-pipes `((?from0 ?from1 ___) ___)
`(?to ___)
(list (lambda () (exec-path `?prog0 `?arg0 ___)) ___))))))
(exec-pipe+ ?args ...)))
((_ (begin ?expr0 ?expr1 ...))
(begin (setup-redirection (= 0 (current-input-port)))
(setup-redirection (= 1 (current-output-port)))
(setup-redirection (= 2 (current-error-port)))
?expr0 ?expr1 ...))
;; epf can be used if you happen to have a program called
;; "epf", "begin", "pipe", etc which you'd like to run.
((_ (epf ?args ...))
(let-syntax ((exec-epf
(syntax-rules ___ ()
((_ (?prog ?arg0 ___) ?redir0 ___)
(begin
(setup-redirection ?redir0) ___
(exec-path `?prog `?arg0 ___))))))
(exec-epf ?args ...)))
;; This is purely for convenience, so you don't need the (epf ...) wrapper
((_ (?prog ?arg0 ...) ?redir0 ...)
(exec-epf (epf (?prog ?arg0 ...) ?redir0 ...)))))
;; TODO: Perhaps expose environment, and mess around with the path so that
;; execve can be used in a sensible way? Scsh has its own PATH, so we could
;; use something similar to that, but it's more work.
(define (exec-path prog . args)
(process-execute (maybe-symbol->string prog) (map maybe-symbol->string args)))
)
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