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97 lines
2.8 KiB
Markdown
97 lines
2.8 KiB
Markdown
# Lambda
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[](https://gezf7g7pd5.execute-api.ap-northeast-1.amazonaws.com/default/source_up_to_date?owner=erg-lang&repos=erg&ref=main&path=doc/EN/syntax/23_lambda.md&commit_hash=b80234b0663f57388f022b86f7c94a85b6250e9a)
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匿名函数是一种无需命名即可动态创建函数对象的语法
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```python
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# `->` 是匿名函数操作符
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# 同 `f x, y = x + y`
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f = (x, y) -> x + y
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# same as `g(x, y: Int): Int = x + y`
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g = (x, y: Int): Int -> x + y
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```
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如果只有一个参数，您可以省略 `()`
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```python
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assert [1, 2, 3].map_collect(i -> i + 1) == [2, 3, 4]
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assert ((i, j) -> [i, j])(1, 2) == [1, 2]
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```
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在下面的情况下，它是 `0..9, (i -> ...)` 而不是 `(0..9, i) -> ...`
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`->` 在左侧只接受一个参数。多个参数作为单个元组接收
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```python
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for 0..9, i: Int ->
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...
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```
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在匿名函数中，由于空格，解析存在差异
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```python
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# 在这种情况下，解释为 `T(() -> Int)`
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i: T() -> Int
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# 在这种情况下，它被解释为 (U()) -> Int
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k: U() -> Int
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```
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匿名函数可以不带参数使用
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```python
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# `=>` 是一个匿名过程操作符
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p! = () => print! # `p!` 被调用
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# `() ->`, `() =>` 有语法糖 `do`, `do!`
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# p! = do! print! "`p!` 被调用
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p!() # `p!` 被调用
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```
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无参数函数可用于延迟初始化
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```python
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time = import "time"
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date = import "datetime"
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now = if! True:
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do!:
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time. sleep! 1000
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date.now!()
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do date.new("1970", "1", "1", "00", "00")
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```
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您还可以键入和模式匹配。正因为如此，`match` 函数大多是借助匿名函数的力量来实现的
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作为 `match` 函数的参数给出的匿名函数从顶部开始按顺序尝试。因此，您应该在顶部描述特殊情况，在底部描述更一般的情况。如果你弄错了顺序，编译器会发出警告(如果可能的话)
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```python
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n = (Complex or Ratio or Int).sample!()
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i = matchn:
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PI -> PI # 如果等于常数 PI
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For (i: 1..10) -> i # 整数从 1 到 10
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(i: Int) -> i # Int
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(c: Complex) -> c.real() # 对于复杂。Int < Complex，但可以回退
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_ -> panic "cannot convert to Int" # 如果以上都不适用。match 必须涵盖所有模式
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```
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错误处理通常也使用 `?` 或 `match` 完成
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```python
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res: ParseResult Int
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matchres:
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i: Int -> i
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err: Error -> panic err.msg
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res2: Result Int, Error
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match res2:
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ok: Not Error -> log Type of ok
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err: Error -> panic err.msg
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```
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## 匿名多相关系数
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```python
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# 与此相同 id|T|x: T = x
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id = |T| x: T -> x
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```
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<p align='center'>
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<a href='./22_naming_rule.md'>上一页</a> | <a href='./24_subroutine.md'>下一页</a>
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</p>
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