7ed716f904
This PR improves the error messages produced by invalid projections and field notation. It also adds a hint to the "function expected" error message noting the argument to which the term is being applied, which can be helpful for debugging spurious "function expected" messages actually caused by syntax errors. --------- Co-authored-by: Joachim Breitner <mail@joachim-breitner.de>
35 lines
853 B
Text
35 lines
853 B
Text
def Set (α : Type) := α → Prop
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def Set.union (s₁ s₂ : Set α) : Set α :=
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fun a => s₁ a ∨ s₂ a
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def FinSet (n : Nat) := Set (Fin n)
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/-!
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The type of `x` is unfolded to find `Set.union`
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-/
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example (x y : FinSet 10) : FinSet 10 :=
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x.union y
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namespace FinSet
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export Set (union)
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end FinSet
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/-!
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Since the types are defeq, this alias works:
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-/
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example (x y : FinSet 10) : FinSet 10 :=
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FinSet.union x y
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/-!
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However, this dot notation fails since there is no `FinSet` argument.
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However, unfolding is the preferred method.
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-/
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/--
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error: Invalid field notation: Function `Set.union` does not have a usable parameter of type `FinSet ...` for which to substitute `x`
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Note: Such a parameter must be explicit, or implicit with a unique name, to be used by field notation
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-/
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#guard_msgs in
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example (x y : FinSet 10) : FinSet 10 :=
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x.union y
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