用Red语言创建地图功能 [英] Creating map function in Red language

问题描述

如何在以下位置创建地图，红色语言.它应该以一个块和一个函数作为参数，并将发送的函数应用于该块的每个成员.我尝试了以下代码:

How can I create map, a higher order function, in Red language. It should take a block and a function as arguments and apply the sent function to each member of block. I tried following code:

Red []
mapfn: function[blk sfn][
    outblk: copy []
    foreach i blk[
        append outblk (sfn i) ]
    outblk ]

; to test: 
myblk: [" this " " is   " " a "  "    line " "for" "   testing " " only   "]
probe mapfn myblk 'reverse 
probe mapfn myblk 'trim

但是它不起作用-它只是发送回原始块，而没有对其进行更改或给出任何错误消息.该如何纠正?

But it is not working - it simply sends back the original block without changing it or giving any error message. How can this be corrected?

推荐答案

在Rebol中，您具有夹层功能 apply

In Rebol you have the mezzanine function apply

>> help apply
USAGE:
    APPLY func block /only 

DESCRIPTION:
     Apply a function to a reduced block of arguments.
     APPLY is a function value.

ARGUMENTS:
     func -- Function value to apply (Type: any-function)
     block -- Block of args, reduced first (unless /only) (Type: block)

REFINEMENTS:
     /only -- Use arg values as-is, do not reduce the block

(SPECIAL ATTRIBUTES)
     throw

请参见适用来源.

只要Red没有本机应用，就可以编写自己的映射函数，例如

As long as Red has no native apply you can write your own mapping function e.g

mapfn: function[blk sfn][
    outblk: copy []
    foreach i blk[
        append outblk sfn copy i 
    ]
    outblk 
]

使用:functionname获取功能

Get the function with :functionname

>> myblk: [" this " " is   " " a "  "    line " "for" "   testing " " only   "]
== [" this " " is   " " a " "    line " "for" "   testing " " only   "]
>> probe mapfn myblk :reverse 
[" siht " "   si " " a " " enil    " "rof" " gnitset   " "   ylno "]
== [" siht " "   si " " a " " enil    " "rof" " gnitset   " "   ylno "]
>> probe mapfn myblk :trim
["this" "is" "a" "line" "for" "testing" "only"]
== ["this" "is" "a" "line" "for" "testing" "only"]
>> 

例如，无法复制所有数据类型的另一种更好的方法是

An alternative and better way as you can not copy all datatypes is e.g.

mapfn: function[blk sfn][
    collect [
        foreach i blk[
            keep sfn i 
        ]
    ]
]

，如果不希望，则以这种方式调用该函数

and call the function this way if no do not want to modify the original

mapfn newblk: copy/deep myblk :reverse

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