lean4-htt/tests/lean/infoFromFailure.lean
2020-10-27 18:29:19 -07:00

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def A.foo {α : Type} [Add α] (a : α) : α × α :=
(a, a + a)
def B.foo {α : Type} (a : α) : α × α :=
(a, a)
open A
open B
set_option trace.Meta.synthInstance true
-- `foo` is overloaded, the case `A.foo` is discarded because we don't have an instance `[Add String]`.
-- However, we still want to see the trace since we used trace.Meta.synthInstance
#check foo "hello"
theorem ex : foo true = (true, true) :=
rfl