summaryrefslogtreecommitdiff
path: root/guix/repl.scm
blob: 0ace5976cfd44a24857b57283988a481c273677e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2018, 2019, 2020 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 repl)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-26)
  #:use-module (ice-9 match)
  #:export (send-repl-response
            machine-repl))

;;; Commentary:
;;;
;;; This module implements the "machine-readable" REPL provided by
;;; 'guix repl -t machine'.  It's a lightweight module meant to be
;;; embedded in any Guile process providing REPL functionality.
;;;
;;; Code:

(define (self-quoting? x)
  "Return #t if X is self-quoting."
  (letrec-syntax ((one-of (syntax-rules ()
                            ((_) #f)
                            ((_ pred rest ...)
                             (or (pred x)
                                 (one-of rest ...))))))
    (one-of symbol? string? keyword? pair? null? array?
            number? boolean? char?)))

(define repl-prompt
  ;; Current REPL prompt or #f.
  (make-parameter #f))

(define (stack->frames stack)
  "Return STACK's frames as a list."
  (unfold (cute >= <> (stack-length stack))
          (cut stack-ref stack <>)
          1+
          0))

(define* (send-repl-response exp output
                             #:key (version '(0 0)))
  "Write the response corresponding to the evaluation of EXP to PORT, an
output port.  VERSION is the client's protocol version we are targeting."
  (define (value->sexp value)
    (if (self-quoting? value)
        `(value ,value)
        `(non-self-quoting ,(object-address value)
                           ,(object->string value))))

  (define (frame->sexp frame)
    `(,(frame-procedure-name frame)
      ,(match (frame-source frame)
         ((_ (? string? file) (? integer? line) . (? integer? column))
          (list file line column))
         (_
          '(#f #f #f)))))

  (define (handle-exception key . args)
    (define reply
      (match version
        ((0 1 (? positive?) _ ...)
         ;; Protocol (0 1 1) and later.
         (let ((stack (if (repl-prompt)
                          (make-stack #t handle-exception (repl-prompt))
                          (make-stack #t))))
           `(exception (arguments ,key ,@(map value->sexp args))
                       (stack ,@(map frame->sexp (stack->frames stack))))))
        (_
         ;; Protocol (0 0).
         `(exception ,key ,@(map value->sexp args)))))

    (write reply output)
    (newline output)
    (force-output output))

  (catch #t
    (lambda ()
      (let ((results (call-with-values
                         (lambda ()
                           (primitive-eval exp))
                       list)))
        (write `(values ,@(map value->sexp results))
               output)
        (newline output)
        (force-output output)))
    (const #t)
    handle-exception))

(define* (machine-repl #:optional
                       (input (current-input-port))
                       (output (current-output-port)))
  "Run a machine-usable REPL over ports INPUT and OUTPUT.

The protocol of this REPL is meant to be machine-readable and provides proper
support to represent multiple-value returns, exceptions, objects that lack a
read syntax, and so on.  As such it is more convenient and robust than parsing
Guile's REPL prompt."
  (define tag
    (make-prompt-tag "repl-prompt"))

  (define (loop exp version)
    (match exp
      ((? eof-object?) #t)
      (exp
       (send-repl-response exp output
                           #:version version)
       (loop (read input) version))))

  (write `(repl-version 0 1 1) output)
  (newline output)
  (force-output output)

  ;; In protocol version (0 0), clients would not send their supported
  ;; protocol version.  Thus, the code below checks for two case: (1) a (0 0)
  ;; client that directly sends an expression to evaluate, and (2) a more
  ;; recent client that sends (() repl-version ...).  This form is chosen to
  ;; be unambiguously distinguishable from a regular Scheme expression.

  (call-with-prompt tag
    (lambda ()
      (parameterize ((repl-prompt tag))
        (match (read input)
          ((() 'repl-version version ...)
           (loop (read input) version))
          (exp
           (loop exp '(0 0))))))
    (const #f)))