用 Red 语言创建地图函数
Creating map function in Red language
如何用 Red 语言创建 map 高阶函数。它应该将一个块和一个函数作为参数,并将发送的函数应用于块的每个成员。我尝试了以下代码:
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
但它不起作用 - 它只是发回原始块而不更改它或给出任何错误消息。如何纠正?
在 Rebol 中你有夹层函数 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
参见来源应用。
只要 Red 没有本地应用,你就可以编写自己的映射函数,例如
mapfn: function[blk sfn][
outblk: copy []
foreach i blk[
append outblk sfn copy i
]
outblk
]
通过:functionname
获取函数
>> 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"]
>>
另一种更好的方法,因为您无法复制所有数据类型,例如
mapfn: function[blk sfn][
collect [
foreach i blk[
keep sfn i
]
]
]
如果没有不想修改原来的就这样调用函数
mapfn newblk: copy/deep myblk :reverse
如何用 Red 语言创建 map 高阶函数。它应该将一个块和一个函数作为参数,并将发送的函数应用于块的每个成员。我尝试了以下代码:
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
但它不起作用 - 它只是发回原始块而不更改它或给出任何错误消息。如何纠正?
在 Rebol 中你有夹层函数 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
参见来源应用。
只要 Red 没有本地应用,你就可以编写自己的映射函数,例如
mapfn: function[blk sfn][
outblk: copy []
foreach i blk[
append outblk sfn copy i
]
outblk
]
通过:functionname
获取函数>> 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"]
>>
另一种更好的方法,因为您无法复制所有数据类型,例如
mapfn: function[blk sfn][
collect [
foreach i blk[
keep sfn i
]
]
]
如果没有不想修改原来的就这样调用函数
mapfn newblk: copy/deep myblk :reverse