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97 lines
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2.8 KiB
Markdown
97 lines
No EOL
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/22_lambda.md&commit_hash=c8932f8fd75cc86f67421bb6b160fffaf7acdd94)
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匿名函數是一種無需命名即可動態創建函數對象的語法
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```python
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# `->` 是匿名函數操作符
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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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如果只有一個參數，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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在下面的情況下，它是 `0..9, (i -> ...)` 而不是 `(0..9, i) -> ...`
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`->` 在左側只接受一個參數。多個參數作為單個元組接收
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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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在匿名函數中，由于空格，解析存在差異
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```python
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# 在這種情況下，解釋為 `T(() -> Int)`
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i: T() -> Int
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# 在這種情況下，它被解釋為 (U()) -> Int
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k: U() -> Int
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```
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匿名函數可以不帶參數使用
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```python
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# `=>` 是一個匿名過程操作符
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p! = () => print! # `p!` 被調用
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# `() ->`, `() =>` 有語法糖 `do`, `do!`
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# p! = do! print! "`p!` 被調用
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p!() # `p!` 被調用
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```
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無參數函數可用于延遲初始化
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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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您還可以鍵入和模式匹配。正因為如此，`match` 函數大多是借助匿名函數的力量來實現的
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作為 `match` 函數的參數給出的匿名函數從頂部開始按順序嘗試。因此，您應該在頂部描述特殊情況，在底部描述更一般的情況。如果你弄錯了順序，編譯器會發出警告(如果可能的話)
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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 # 如果等于常數 PI
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For (i: 1..10) -> i # 整數從 1 到 10
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(i: Int) -> i # Int
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(c: Complex) -> c.real() # 對于復雜。Int < Complex，但可以回退
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_ -> panic "cannot convert to Int" # 如果以上都不適用。match 必須涵蓋所有模式
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```
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錯誤處理通常也使用 `?` 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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## 匿名多相關系數
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```python
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# 與此相同 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='./21_naming_rule.md'>上一頁</a> | <a href='./23_subroutine.md'>下一頁</a>
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</p> |