Documentation

Lean.Meta.CoeAttr

The @[coe] attribute, used to delaborate coercion functions as #

When writing a coercion, if the pattern

@[coe]
def A.toB (a : A) : B := sorry

instance : Coe A B where coe := A.toB

is used, then A.toB a will be pretty-printed as ↑a.

The different types of coercions that are supported by the coe attribute.

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      Information associated to a coercion function to enable sensible delaboration.

      • numArgs : Nat

        The number of arguments to the coercion function

      • coercee : Nat

        The argument index that represents the value being coerced

      • type : CoeFnType

        The type of coercion

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          The environment extension for tracking coercion functions for delaboration

          Lookup the coercion information for a given function

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            Add name to the coercion extension and add a coercion delaborator for the function.

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