Colon (:)

:: Header

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Placed at the end of a block header. A header has syntax that matches the way the block is called. It indicates the block type, and number and structure of inputs.

    "xy" {a‿b _op c: b} ∞
'y'

Multiple bodies are searched in order to find one with a matching header.

    F ← {m Fn n: m+Fn n;  𝕊n: 2×n;  𝕊⁼𝕩: 𝕩÷2}

    F 3      # 𝕊n
6

    F⁼ 6     # 𝕊⁼𝕩
3

    10 F 3   # m Fn n
16