scheme - 如何捕获语法异常

Question

我想通过一个测试语法异常的宏来扩展 srfi-78。我想要这样的东西:

#! /usr/bin/env scheme-script
#!r6rs

(import (rnrs) (srfi :78 lightweight-testing))

; the macros I want to test
(define-syntax some-macros
  (syntax-rules ()
    [(_) 'ok]))

; the extension to srfi-78
(define-syntax check-exception
  (syntax-rules ()
        ; ... some code ...
        ))

; tests

; prints "correct" or someting like that
(check (some-macros) => 'ok)

; should print "correct" (i. e. the test passed)
(check-exception (some-macros 'arg)) 

; should print "error"
; (i. e. the exception was not thrown as expected)
(check-exception (some-macros)) 

有可能吗？如果没有，您将如何为宏编写测试？

我知道 test-read-eval-string来自 srfi-64。它接受一个字符串，将它转换成一个形式并在初始环境中评估这个形式。我想要一个宏来评估当前环境中的给定形式并捕获异常。

Answer 1

唯一可移植的方法是通过 eval 调用代码，并将其包装在一个守卫中。

例如:

(define (safe-eval code env)
  (guard [e [(syntax-violation? e) (display e)]]
    (eval code env)))

用法:

> (safe-eval '(let a v) (environment '(rnrs)))
&who: let
&message: "invalid syntax"
&syntax:
  form: (let a v)
  subform: #f