Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
b4a290a203
Before this commit, `Simproc`s were defined as `Expr -> SimpM (Option Step)`, where `Step` is inductively defined as follows: ``` inductive Step where | visit : Result → Step | done : Result → Step ``` Here, `Result` is a structure containing the resulting expression and a proof demonstrating its equality to the input. Notably, the proof is optional; in its absence, `simp` assumes reflexivity. A simproc can: - Fail by returning `none`, indicating its inapplicability. In this case, the next suitable simproc is attempted, along with other simp extensions. - Succeed and invoke further simplifications using the `.visit` constructor. This action returns control to the beginning of the simplification loop. - Succeed and indicate that the result should not undergo further simplifications. However, I find the current approach unsatisfactory, as it does not align with the methodology employed in `Transform.lean`, where we have the type: ``` inductive TransformStep where /-- Return expression without visiting any subexpressions. -/ | done (e : Expr) /-- Visit expression (which should be different from current expression) instead. The new expression `e` is passed to `pre` again. -/ | visit (e : Expr) /-- Continue transformation with the given expression (defaults to current expression). For `pre`, this means visiting the children of the expression. For `post`, this is equivalent to returning `done`. -/ | continue (e? : Option Expr := none) ``` This type makes it clearer what is going on. The new `Simp.Step` type is similar but use `Result` instead of `Expr` because we need a proof. |
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