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;;; srfi-35.scm --- Conditions -*- coding: utf-8 -*-
;; Copyright (C) 2007-2011, 2017, 2022 Free Software Foundation, Inc.
;;
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;;
;; This library 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
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Author: Ludovic Courtès <[email protected]>
;;; Commentary:
;; This is an implementation of SRFI-35, "Conditions". Conditions are a
;; means to convey information about exceptional conditions between parts of
;; a program.
;;; Code:
(define-module (srfi srfi-35)
#:use-module (ice-9 match)
#:use-module (ice-9 exceptions)
#:re-export ((make-exception-type . make-condition-type)
(exception-type? . condition-type?)
(exception? . condition?)
(make-exception . make-compound-condition)
(&exception . &condition)
&message
(exception-with-message? . message-condition?)
(exception-message . condition-message)
(&error . &serious)
(error? . serious-condition?)
(external-error? . error?))
#:re-export-and-replace ((&external-error . &error))
#:export (make-condition
define-condition-type
condition-has-type?
condition-ref
extract-condition
condition))
(cond-expand-provide (current-module) '(srfi-35))
(define (make-condition type . field+value)
"Return a new condition of type TYPE with fields initialized as specified
by FIELD+VALUE, a sequence of field names (symbols) and values."
(unless (exception-type? type)
(scm-error 'wrong-type-arg "make-condition" "Not a condition type: ~S"
(list type) #f))
(let* ((fields (record-type-fields type))
(uninitialized (list 'uninitialized))
(inits (make-vector (length fields) uninitialized)))
(let lp ((args field+value))
(match args
(()
(let lp ((i 0) (fields fields))
(when (< i (vector-length inits))
(when (eq? (vector-ref inits i) uninitialized)
(error "field not specified" (car fields)))
(lp (1+ i) (cdr fields))))
(apply make-struct/simple type (vector->list inits)))
(((and (? symbol?) field) value . args)
(let lp ((i 0) (fields fields))
(when (null? fields)
(error "unknown field" field))
(cond
((eq? field (car fields))
(unless (eq? (vector-ref inits i) uninitialized)
(error "duplicate initializer" field))
(vector-set! inits i value))
(else
(lp (1+ i) (cdr fields)))))
(lp args))
(inits
(scm-error 'wrong-type-arg "make-condition"
"Bad initializer list tail: ~S"
(list inits) #f))))))
(define (condition-has-type? c type)
"Return true if condition C has type TYPE."
(unless (exception-type? type)
(scm-error 'wrong-type-arg "condition-has-type?" "Not a condition type: ~S"
(list type) #f))
(or-map (record-predicate type) (simple-exceptions c)))
;; Precondition: C is a simple condition.
(define (simple-condition-ref c field-name not-found)
(match (list-index (record-type-fields (struct-vtable c)) field-name)
(#f (not-found))
(pos (struct-ref c pos))))
(define (condition-ref c field-name)
"Return the value of the field named FIELD-NAME from condition C."
(let lp ((conditions (simple-exceptions c)))
(match conditions
(() (error "invalid field name" field-name))
((c . conditions)
(simple-condition-ref c field-name (lambda () (lp conditions)))))))
(define (make-condition-from-values type values)
(apply make-struct/simple type values))
(define (extract-condition c type)
"Return a condition of condition type TYPE with the field values specified
by C."
(unless (exception-type? type)
(scm-error 'wrong-type-arg "extract-condition" "Not a condition type: ~S"
(list type) #f))
(let ((pred (record-predicate type)))
(or-map (lambda (x) (and (pred x) x)) (simple-exceptions c))))
(define-syntax define-condition-type
(lambda (s)
(syntax-case s ()
((_ type parent predicate (field accessor) ...)
;; The constructor is unused, but generate a new name for each
;; condition to avoid '-Wshadowed-toplevel' warnings when several
;; condition types are defined in the same compilation unit.
(with-syntax ((unused-constructor
(datum->syntax
#'type
(symbol-append '#{ make-}# (syntax->datum #'type)))))
#'(define-exception-type type parent
unused-constructor predicate
(field accessor) ...))))))
(define-syntax condition-instantiation
;; Build the `(make-condition type ...)' call.
(syntax-rules ()
((_ type (out ...))
(make-condition type out ...))
((_ type (out ...) (field-name field-value) rest ...)
(condition-instantiation type (out ... 'field-name field-value) rest ...))))
(define-syntax condition
(syntax-rules ()
((_ (type field ...))
(condition-instantiation type () field ...))
((_ (type field ...) ...)
(make-exception (condition-instantiation type () field ...)
...))))
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