重新设置和取消设置（可选）参数
我想创建一个 do-libs 通用函数来自动加载 rebol 头文件中列出的一堆库。我想让参数可选，但在后面的情况下它不起作用，为什么？
Rebol[
libs: [
lib1/lib11.r
lib1/lib12.r
lib2/lib21.r
]
]
do-libs 'libs ; works
do-libs ; doesn't work
和：
do-libs: func[libs [word! unset!]][
if/else value? 'libs [
foreach lib system/script/header/:libs [
if/else file? lib [
do lib
][
do file: to-rebol-file mold lib
]
]
][
;case with no parameter
do-libs 'libs
]
]
I want to create a do-libs generic function to automatically load a bunch of libs listed in rebol header files. I want to make the parameter optional but in that later case it doesn't work why ?
Rebol[
libs: [
lib1/lib11.r
lib1/lib12.r
lib2/lib21.r
]
]
do-libs 'libs ; works
do-libs ; doesn't work
with:
do-libs: func[libs [word! unset!]][
if/else value? 'libs [
foreach lib system/script/header/:libs [
if/else file? lib [
do lib
][
do file: to-rebol-file mold lib
]
]
][
;case with no parameter
do-libs 'libs
]
]
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评论（1）
我不是这方面的专家，但我的理解是，为了创建一个允许省略参数的函数，它必须是一个文字参数，例如，
do-libs: func [ 'libs [word! unset!] ] [ ; blah blah ]请注意，libs 参数是一个 <代码>lit-word！。这也意味着您必须按如下方式调用此函数：
或者
但是，请小心这一点。 REBOL 不尊重新线。如果你说：
它会将 3 视为 do-libs 的参数，并且你的函数调用将失败。如果你说它
会将
print视为do-libs的'libs参数。事实上，REBOL 将上述内容解释为底线是参数省略是针对 REBOL 的交互模式的。 你不应该用它来做你想做的事情。相反，您的函数可能应该如下所示：
do-libs: func [ /name 'word [word!] ] [ if none? name [ word: 'libs ] ; and so on ]现在您可以说
OR
这是更自然、更惯用的 REBOL。一般来说，应该使用改进来传递可选参数。当参数的数量可能未知或不受限制时，应使用
block!。由于 REBOL 解释器的工作方式，REBOL 不太可能支持许多其他语言（C、C++、Ruby 等）所具有的“param array”样式参数。解释器无法知道参数列表在哪里结束，除非整个表达式放在括号中，如下所示：
I'm not an expert in this, but my understanding is that in order to create a function that allows argument omission, it has to be a literal argument, e.g.,
do-libs: func [ 'libs [word! unset!] ] [ ; blah blah ]Note that the libs argument is a
lit-word!. This also means you would have to call this function as follows:OR
However, be careful with this. REBOL does not respect new lines. If you say:
It will regard 3 as an argument to
do-libsand your function call will fail. If you sayIt will regard
printas the'libsargument ofdo-libs. In fact, REBOL interprets the above asThe bottom line is that argument omission is intended for REBOL's interactive mode. You shouldn't use it to do what you're trying to do. Instead, your function should probably look like this:
do-libs: func [ /name 'word [word!] ] [ if none? name [ word: 'libs ] ; and so on ]Now you can say
OR
This is more natural, idiomatic REBOL. In general, refinements should be used to pass optional arguments. When the number of arguments is potentially unknown or unlimited, a
block!should be used.Because of how the REBOL interpreter works, it's very unlikely that REBOL will ever support the "param array" style arguments that many other languages (C, C++, Ruby, etc.) have. The interpreter would have no way of knowing where the argument list ends, unless the entire expression was placed in parentheses like so: