72 lines
1.5 KiB
Plaintext
72 lines
1.5 KiB
Plaintext
;; if let: the block runs when the pattern matches, its names bound there only.
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data Shape
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Rect(w: i32, h: i32)
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Dot
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enum Dir
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north = 0
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south = 1
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fn describe(o: Option(i32), k: i32) -> i32
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if let Some(g) = o
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g + 1
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elif k > 5
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100
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else
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0
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fn first(xs: [3 i32]) -> i32
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if let Some(x) = get(xs, 0) then x else -1
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;; elif let: the rest of the chain is the else of an if let.
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fn pick(a: Option(i32), b: Option(i32), k: i32) -> i32
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if let Some(x) = a
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x
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elif let Some(y) = b
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y * 10
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elif k > 5
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100
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else
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0
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;; Nested: a pattern tested inside the block of another.
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fn area(s: Option(Shape)) -> i32
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if let Some(x) = s
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if let Rect(w, h) = x
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w * h
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else
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-1
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else
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-2
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fn main()
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let g = 7
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println(describe(Some(4), 0))
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println(describe(None, 9))
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println(describe(None, 1))
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println(first([9, 8, 7]))
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println(pick(Some(1), None, 0))
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println(pick(None, Some(2), 0))
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println(pick(None, None, 9))
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println(pick(None, None, 1))
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;; Shadowing: g is the payload inside the block and the outer g after it.
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if let Some(g) = Some(1)
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println(g)
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println(g)
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;; Any match pattern.
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if let None = get([1, 2], 5)
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println("absent")
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if let :north = Dir.north
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println("north")
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println(area(Some(Shape.Rect{.w 2 .h 3})))
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println(area(Some(Shape.Dot)))
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println(area(None))
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;; when on one line and with a block.
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let w = when g > 3 then g * 2
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match w
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Some(v) -> println(v)
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None -> println("none")
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when g > 1
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println("when block")
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