50 lines
1.7 KiB
Text
50 lines
1.7 KiB
Text
/-
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Copyright (c) 2016 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Leonardo de Moura
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Helper tactic for showing that a type has decidable equality.
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-/
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prelude
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import init.meta.contradiction_tactic init.meta.constructor_tactic
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import init.meta.injection_tactic init.meta.relation_tactics
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namespace tactic
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open expr environment list
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/- Retrieve the name of the type we are building an inhabitant instance for. -/
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private meta_definition get_inhabited_type_name : tactic name :=
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do {
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(app (const n ls) t) ← target >>= whnf | failed,
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when (n ≠ `inhabited) failed,
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(const I ls) ← return (get_app_fn t) | failed,
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return I }
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<|>
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fail "mk_inhabited_instance tactic failed, target type is expected to be of the form (inhabited ...)"
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/- Try to synthesize constructor argument using type class resolution -/
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private meta_definition mk_inhabited_arg : tactic unit :=
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do tgt ← target,
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inh ← mk_app `inhabited [tgt],
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inst ← mk_instance inh,
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mk_app `inhabited.value [inst] >>= exact
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private meta_definition try_constructors : nat → nat → tactic unit
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| 0 n := failed
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| (i+1) n :=
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do {constructor_idx (n - i), all_goals mk_inhabited_arg, now}
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<|>
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try_constructors i n
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meta_definition mk_inhabited_instance : tactic unit :=
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do
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I ← get_inhabited_type_name,
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env ← get_env,
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n : nat ← return $ length (constructors_of env I),
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when (n = 0) (fail $ "mk_inhabited_instance failed, type '" ++ to_string I ++ "' does not have constructors"),
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constructor,
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(try_constructors n n)
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<|>
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(fail $ "mk_inhabited_instance failed, failed to build instance using all constructors of '" ++ to_string I ++ "'")
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end tactic
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