19bebfc22f
Makes the error messages report on RHSs and LHSs that do not match the expected values when the relations are defeq. If the relations are not defeq, the error message now no longer mentions the value of the whole `calc` expression. Adds a field to `mkCoe` with an optional callback to use to generate error messages. Note: it is tempting to try to make use of expected types when elaborating the `calc` expression, but this runs into issue #2073. Closes #4318
105 lines
1.9 KiB
Text
105 lines
1.9 KiB
Text
/-!
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# Better `calc` error messages
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RFC https://github.com/leanprover/lean4/issues/4318
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-/
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axiom testSorry {α : Sort _} : α
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/-!
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Term-mode `calc`. Errors about LHS and RHS not matching expected type.
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-/
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/--
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error: invalid 'calc' step, left-hand side is
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1 + n - n : Nat
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but is expected to be
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0 : Nat
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-/
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#guard_msgs in
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example (n : Nat) : 0 = 1 :=
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calc
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1 + n - n = 1 := testSorry
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/--
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error: invalid 'calc' step, right-hand side is
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n - n : Nat
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but is expected to be
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1 : Nat
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-/
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#guard_msgs in
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example (n : Nat) : 0 = 1 :=
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calc
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0 = n - n := testSorry
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/--
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error: 'calc' expression has type
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0 = 1 : Prop
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but is expected to have type
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0 < 1 : Prop
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-/
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#guard_msgs in
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example : 0 < 1 :=
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calc
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0 = 1 := testSorry
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/-!
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Tactic-mode `calc`. LHS failure.
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-/
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/--
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error: invalid 'calc' step, left-hand side is
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1 + n - n : Nat
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but is expected to be
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0 : Nat
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-/
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#guard_msgs in
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example (n : Nat) : 0 = 1 := by
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calc
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1 + n - n = 1 := testSorry
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/-!
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Tactic mode `calc`. RHS failure, but calc extension succeeds.
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-/
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example (n : Nat) : 0 ≤ 1 := by
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calc 0
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_ ≤ n - n := testSorry
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guard_target =ₛ n - n ≤ 1
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exact testSorry
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/-!
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Tactic mode `calc`. Calc extension fails due to expected type mismatch, so report original failure.
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-/
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/--
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error: 'calc' expression has type
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0 < n - n : Prop
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but is expected to have type
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0 ≤ 1 : Prop
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-/
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#guard_msgs in
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example (n : Nat) : 0 ≤ 1 := by
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calc
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0 < n - n := testSorry
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/-!
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Tactic mode `calc`. Calc extension fails due to nontransitivity, so report original failure.
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-/
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/--
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error: invalid 'calc' step, right-hand side is
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1 : Nat
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but is expected to be
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2 : Nat
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-/
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#guard_msgs in
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example (n : Nat) : 0 ≠ 2 := by
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calc 0
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_ ≠ 1 := testSorry
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/-!
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Tactic mode `calc`. Calc extension succeeds.
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-/
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#guard_msgs in
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example : 0 < 1 := by
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calc 0
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_ ≤ 1 := testSorry
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guard_target =ₛ 1 < 1
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exact testSorry
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