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311 lines
5.6 KiB
Markdown
311 lines
5.6 KiB
Markdown
# 快速瀏覽
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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/quick_tour.md&commit_hash=44d7784aac3550ba97c8a1eaf20b9264b13d4134)
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`syntax` 下面的文檔是為了讓編程初學者也能理解而編寫的
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對于已經掌握 Python、Rust、Haskell 等語言的人來說，可能有點啰嗦
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所以，這里是 Erg 語法的概述
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請認為未提及的部分與 Python 相同
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## 基本計算
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Erg 有一個嚴格的類型。但是, 由于類和Trait提供的靈活性, 類型會自動轉換為子類型(有關詳細信息，請參閱 [API])
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另外，不同的類型可以相互計算，只要類型是數值類型即可
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```python
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a = 1 # 1: Nat
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b = a - 10 # -9: Int
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c = b / 2 # -4.5: Float
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d = c * 0 # -0.0: Float
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e = f // 2 # 0: Nat
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```
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如果您不想允許這些隱式類型轉換，您可以在聲明時指定類型以在編譯時將它們檢測為錯誤
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```python
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a = 1
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b: Int = a / 2
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# 錯誤信息
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Error[#0047]: File <stdin>, line 1, in <module>
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2│ b: Int = int / 2
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^
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類型錯誤: ratio的類型不匹配:
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期待: Int
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但找到: Float
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```
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## 布爾類型
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`True` 和 `False` 是 Boolean 類型的單例，但它們也可以轉換為 Int 類型
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因此，如果它們是 Int 類型，則可以進行比較，但與其他類型比較會導致錯誤
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```python
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True == 1 # OK
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False == 0 # OK
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True == 1.0 # NG
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False == 0.0 # NG
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True == "a" # NG
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```
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## 變量，常量
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變量用 `=` 定義。與 Haskell 一樣，變量一旦定義就不能更改。但是，它可以在另一個范圍內被遮蔽
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```python
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i = 0
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if True:
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i = 1
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assert i == 0
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```
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任何以大寫字母開頭的都是常數。只有可以在編譯時計算的東西才能是常量
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此外，自定義以來，常量在所有范圍內都是相同的
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```python
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PI = 3.141592653589793
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match random.random!(0..10):
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PI ->
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log "You get PI, it's a miracle!"
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```
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## 類型聲明
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與 Python 不同的是，只能先聲明變量類型
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當然，聲明的類型和實際分配的對象的類型必須兼容
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```python
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i: Int
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i = 10
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```
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## 函數
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你可以像在 Haskell 中一樣定義它
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```python
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fib 0 = 0
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fib 1 = 1
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fib n = fib(n - 1) + fib(n - 2)
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```
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匿名函數可以這樣定義:
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```python
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i -> i + 1
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assert [1, 2, 3].map(i -> i + 1).to_arr() == [2, 3, 4]
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```
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## 運算符
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特定于 Erg 的運算符是:
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### 變異運算符 (!)
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這就像 Ocaml 中的`ref`
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```python
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i = !0
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i.update! x -> x + 1
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assert i == 1
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```
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## 程序
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具有副作用的子例程稱為過程，并標有`!`
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您不能在函數中調用過程
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```python
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print! 1 # 1
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```
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## 泛型函數(多相關)
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```python
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id|T|(x: T): T = x
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id(1): Int
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id("a"): Str
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```
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## 記錄
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您可以使用類似 ML 的語言中的記錄等價物(或 JS 中的對象字面量)
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```python
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p = {x = 1; y = 2}
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assert p.x == 1
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```
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## 所有權
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Ergs 由可變對象(使用 `!` 運算符突變的對象)擁有，并且不能從多個位置重寫
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```python
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i = !0
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j = i
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assert j == 0
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i# 移動錯誤
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```
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另一方面，不可變對象可以從多個位置引用
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## 可見性
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使用 `.` 前綴變量使其成為公共變量并允許從外部模塊引用它
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```python
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# foo.er
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.x = 1
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y = 1
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```
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```python
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foo = import "foo"
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assert foo.x == 1
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foo.y # 可見性錯誤
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```
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## 模式匹配
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### 變量模式
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```python
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# 基本任務
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i = 1
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# with 類型
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i: Int = 1
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# 函數
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fn x = x + 1
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fn: Int -> Int = x -> x + 1
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```
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### 文字模式
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```python
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# 如果 `i` 在編譯時無法確定為 1，則發生 類型錯誤
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# 簡寫: `_ {1} = i`
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1 = i
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# 簡單的模式匹配
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match x:
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1 -> "1"
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2 -> "2"
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_ -> "other"
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# 斐波那契函數
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fib0 = 0
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fib1 = 1
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fibn: Nat = fibn-1 + fibn-2
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```
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### 常量模式
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```python
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PI = 3.141592653589793
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E = 2.718281828459045
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num = PI
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name = match num:
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PI -> "pi"
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E -> "e"
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_ -> "unnamed"
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```
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### 丟棄(通配符)模式
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```python
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_ = 1
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_: Int = 1
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right(_, r) = r
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```
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### 可變長度模式
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與稍后描述的元組/數組/記錄模式結合使用
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```python
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[i, *j] = [1, 2, 3, 4]
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assert j == [2, 3, 4]
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first|T|(fst: T, *rest: T) = fst
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assert first(1, 2, 3) == 1
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```
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### 元組模式
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```python
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(i, j) = (1, 2)
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((k, l), _) = ((1, 2), (3, 4))
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# 如果不嵌套，() 可以省略(1, 2 被視為(1, 2))
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m, n = 1, 2
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```
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### 數組模式
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```python
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length [] = 0
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length [_, *rest] = 1 + length rest
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```
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#### 記錄模式
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```python
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{sin; cos; tan} = import "math"
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{*} = import "math" # 全部導入
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person = {name = "John Smith"; age = 20}
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age = match person:
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{name = "Alice"; _} -> 7
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{_; age} -> age
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```
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### 數據類模式
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```python
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Point = Inherit {x = Int; y = Int}
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p = Point::{x = 1; y = 2}
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Point::{x; y} = p
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```
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## 理解(Comprehensions)
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```python
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odds = [i | i <- 1..100; i % 2 == 0]
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```
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## Class
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Erg 不支持多重繼承
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## Trait
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它們類似于 Rust Trait，但在更字面意義上，允許組合和解耦，并將屬性和方法視為平等
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此外，它不涉及實施
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```python
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XY = Trait {x = Int; y = Int}
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Z = Trait {z = Int}
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XYZ = XY and Z
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Show = Trait {show: Self.() -> Str}
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@Impl XYZ, Show
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Point = Class {x = Int; y = Int; z = Int}
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Point.
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...
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```
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## 修補
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您可以為類和Trait提供實現
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## 篩子類型
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謂詞表達式可以是類型限制的
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```python
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Nat = {I: Int | I >= 0}
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```
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## 帶值的參數類型(依賴類型)
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```python
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a: [Int; 3]
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b: [Int; 4]
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a + b: [Int; 7]
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```
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