02c8c2f9e1
This PR implements first-class support for nondependent let expressions in the elaborator; recall that a let expression `let x : t := v; b` is called *nondependent* if `fun x : t => b` typechecks, and the notation for a nondependent let expression is `have x := v; b`. Previously we encoded `have` using the `letFun` function, but now we make use of the `nondep` flag in the `Expr.letE` constructor for the encoding. This has been given full support throughout the metaprogramming interface and the elaborator. Key changes to the metaprogramming interface: - Local context `ldecl`s with `nondep := true` are generally treated as `cdecl`s. This is because in the body of a `have` expression the variable is opaque. Functions like `LocalDecl.isLet` by default return `false` for nondependent `ldecl`s. In the rare case where it is needed, they take an additional optional `allowNondep : Bool` flag (defaults to `false`) if the variable is being processed in a context where the value is relevant. - Functions such as `mkLetFVars` by default generalize nondependent let variables and create lambda expressions for them. The `generalizeNondepLet` flag (default true) can be set to false if `have` expressions should be produced instead. **Breaking change:** Uses of `letLambdaTelescope`/`mkLetFVars` need to use `generalizeNondepLet := false`. See the next item. - There are now some mapping functions to make telescoping operations more convenient. See `mapLetTelescope` and `mapLambdaLetTelescope`. There is also `mapLetDecl` as a counterpart to `withLetDecl` for creating `let`/`have` expressions. - Important note about the `generalizeNondepLet` flag: it should only be used for variables in a local context that the metaprogram "owns". Since nondependent let variables are treated as constants in most cases, the `value` field might refer to variables that do not exist, if for example those variables were cleared or reverted. Using `mapLetDecl` is always fine. - The simplifier will cache its let dependence calculations in the nondep field of let expressions. - The `intro` tactic still produces *dependent* local variables. Given that the simplifier will transform lets into haves, it would be surprising if that would prevent `intro` from creating a local variable whose value cannot be used. Note that nondependence of lets is not checked by the kernel. To external checker authors: If the elaborator gets the nondep flag wrong, we consider this to be an elaborator error. Feel free to typecheck `letE n t v b true` as if it were `app (lam n t b default) v` and please report issues. This PR follows up from #8751, which made sure the nondep flag was preserved in the C++ interface.
51 lines
2.1 KiB
Text
51 lines
2.1 KiB
Text
example (f : Nat → Nat) : (if f x = 0 then f x else f x + 1) + f x = y := by
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simp (config := { contextual := true })
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guard_target =ₛ (if f x = 0 then 0 else f x + 1) + f x = y
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sorry
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example (f : Nat → Nat) : f x = 0 → f x + 1 = y := by
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simp (config := { contextual := true })
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guard_target =ₛ f x = 0 → 1 = y
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sorry
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example (f : Nat → Nat) : let _ : f x = 0 := sorryAx _ false; f x + 1 = y := by
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simp (config := { contextual := true, zeta := false, zetaUnused := false })
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guard_target =ₛ have _ : f x = 0 := sorryAx _ false; 1 = y
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sorry
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def overlap : Nat → Nat
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| 0 => 0
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| 1 => 1
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| n+1 => overlap n
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example : (if (n = 0 → False) then overlap (n+1) else overlap (n+1)) = overlap n := by
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simp (config := { contextual := true }) only [overlap]
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guard_target =ₛ (if (n = 0 → False) then overlap n else overlap (n+1)) = overlap n
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sorry
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example : (if (n = 0 → False) then overlap (n+1) else overlap (n+1)) = overlap n := by
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-- The following tactic should because the default discharger only uses assumptions available
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-- when `simp` was invoked unless `contextual := true`
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fail_if_success simp only [overlap]
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guard_target =ₛ (if (n = 0 → False) then overlap (n+1) else overlap (n+1)) = overlap n
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sorry
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example : (if (n = 0 → False) then overlap (n+1) else overlap (n+1)) = overlap n := by
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-- assumption is not a well-behaved discharger, and the following should still work as expected
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simp (discharger := assumption) only [overlap]
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guard_target =ₛ (if (n = 0 → False) then overlap n else overlap (n+1)) = overlap n
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sorry
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opaque p : Nat → Bool
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opaque g : Nat → Nat
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@[simp] theorem g_eq (h : p x) : g x = x := sorry
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example : (if p x then g x else g x + 1) + g x = y := by
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simp (discharger := assumption)
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guard_target =ₛ (if p x then x else g x + 1) + g x = y
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sorry
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example : (let _ : p x := sorryAx _ false; g x + 1 = y) ↔ g x = y := by
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simp (config := { zeta := false, zetaUnused := false }) (discharger := assumption)
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guard_target =ₛ (have _ : p x := sorryAx _ false; x + 1 = y) ↔ g x = y
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sorry
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