在 Chez Scheme 中显示乱序
display working out of order in Chez Scheme
我在 Mac 上使用 chez 9.5.4。
以下代码：
;; demo.ss
(map display (list "this " "is " "weird "))
这样做：
$ chez --script demo.ss
weird this is
为什么意外的尤达？
我该如何防止这种情况发生？
它在 Chicken Scheme 中按预期工作。
As answered by u/bjoli on reddit:
Your code is relying on unspecified behaviour: The order of map is unspecified.
You want for-each.
Chez has no stack overflow (like racket or guile). Doing a right fold with map means no (reverse ...) At the end. It is faster, except in some continuation-heavy code.
Schemes without the expanding stack optimization all do a left fold. Like chicken.
简而言之，这正是 map 所做的。
根据 r7rs-small 规范，https://small.r7rs.org/attachment/r7rs.pdf 第 51 页：
The dynamic order in which proc is applied to
the elements of the list s is unspecified.
这是因为 map 旨在通过对每个元素应用纯函数来转换列表。 map 的唯一作用应该是它的结果列表。
正如 divs1210 引用 u/bjoli 指出的那样，Scheme 还定义了一个过程来完成您想要的事情。事实上，for-each 在 r7rs-small pdf 的同一页上有描述！它说：
The arguments to for-each are like the arguments to map,
but for-each calls proc for its side effects rather than for
its values. Unlike map, for-each is guaranteed to call proc
on the elements of the list s in order from the first ele-
ment(s) to the last, and the value returned by for-each
is unspecified.
我在 Mac 上使用 chez 9.5.4。
以下代码：
;; demo.ss
(map display (list "this " "is " "weird "))
这样做：
$ chez --script demo.ss
weird this is
为什么意外的尤达？
我该如何防止这种情况发生？
它在 Chicken Scheme 中按预期工作。
As answered by u/bjoli on reddit:
Your code is relying on unspecified behaviour: The order of map is unspecified.
You want for-each.
Chez has no stack overflow (like racket or guile). Doing a right fold with map means no (reverse ...) At the end. It is faster, except in some continuation-heavy code.
Schemes without the expanding stack optimization all do a left fold. Like chicken.
简而言之，这正是 map 所做的。
根据 r7rs-small 规范，https://small.r7rs.org/attachment/r7rs.pdf 第 51 页：
The dynamic order in which proc is applied to the elements of the list s is unspecified.
这是因为 map 旨在通过对每个元素应用纯函数来转换列表。 map 的唯一作用应该是它的结果列表。
正如 divs1210 引用 u/bjoli 指出的那样，Scheme 还定义了一个过程来完成您想要的事情。事实上，for-each 在 r7rs-small pdf 的同一页上有描述！它说：
The arguments to for-each are like the arguments to map, but for-each calls proc for its side effects rather than for its values. Unlike map, for-each is guaranteed to call proc on the elements of the list s in order from the first ele- ment(s) to the last, and the value returned by for-each is unspecified.