d8accf47b3
This PR changes "structure-like" terminology to "non-recursive structure" across internal documentation, error messages, the metaprogramming API, and the kernel, to clarify Lean's type theory. A *structure* is a one-constructor inductive type with no indices — these can be created by either the `structure` or `inductive` commands — and are supported by the primitive `Expr.proj` projections. Only *non-recursive* structures have an eta conversion rule. The PR description contains the APIs that were renamed. Addresses RFC #5891, which proposed this rename. The change is motivated by the need to distinguish between `structure`-defined structures, structures, and non-recursive structures. Especially since #5783, which enabled the `structure` command to define recursive structures, "structure-like" has been easy to misunderstand. Changes: - Kernel: `is_structure_like()` -> `is_non_rec_structure()` - `Lean.isStructureLike` -> `Lean.isNonRecStructure` - `Lean.matchConstStructLike` -> `Lean.matchConstNonRecStructure` - `Lean.getStructureLikeCtor?` -> `Lean.getNonRecStructureCtor?` - `Lean.getStructureLikeNumFields` -> `Lean.getNonRecStructureNumFields` - `Lean.Expr.proj`: extended and corrected documentation (note: despite the fact that not every projection can be written as a recursor application, I left in this claim since it seems good to document a more-restrictive specification, and some users have requested the kernel be more restrictive in this way) Closes #5891
29 lines
660 B
Text
29 lines
660 B
Text
/-!
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# Projections on types without fields
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https://github.com/leanprover/lean4/issues/9312
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Ensures that a suitable error message is displayed when attempting to project from a type that has
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no fields.
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-/
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structure MyEmpty where
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/--
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error: Invalid projection: Projections extract constructor fields for one-constructor inductive types. The expression
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{ }
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has type `MyEmpty` which has no fields.
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-/
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#guard_msgs in
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#check (MyEmpty.mk).1
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inductive T where
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| a
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/--
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error: Invalid projection: Projections extract constructor fields for one-constructor inductive types. The expression
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T.a
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has type `T` which has no fields.
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-/
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#guard_msgs in
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#check (T.a).1
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