[Agda] [new-reflection] unsolved metas in induction

Martin Stone Davis martin.stone.davis at gmail.com
Fri Jan 22 21:57:07 CET 2016


I'm a newbie to reflection in Agda and am excited to learn the
new-reflection machinery. I'm starting by working through the example of
induction in Tactic.Nat.

  induction-example : ∀ n → sum (downFrom n) * 2 ≡ n * (n + 1)
  induction-example = induction

I tried to figure out what the induction macro is doing and came up with
this:

  by-hand : ∀ n → sum (downFrom n) * 2 ≡ n * (n + 1)
  by-hand = nat-induction (λ n → sum (downFrom n) * 2 ≡ n * (n + 1)) auto
(λ n eq → by eq)

So far, great. I also tried:

  unsolved-metas : ∀ n → sum (downFrom n) * 2 ≡ n * (n + 1)
  unsolved-metas n = induction n

but that produces 3 yellow-highlighted errors. However, there are no such
problems in the "by-hand" version:

  by-hand-2 : ∀ n → sum (downFrom n) * 2 ≡ n * (n + 1)
  by-hand-2 n = nat-induction (λ n → sum (downFrom n) * 2 ≡ n * (n + 1))
auto (λ n eq → by eq) n

I'm confused. TIA for help in understanding this.
--
Martin Stone Davis

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