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lean4/tests/elabissues/error_aux_decl_exists.lean
Leonardo de Moura 7d7cd1a7c9 doc: document issue
cc @dselsam
2020-02-18 10:52:12 -08:00

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Lean4

/-
Sub-optimal error message.
The implementation detail that an auxiliary function `foo._main` leaks,
when there is a simple explanation for the problem that doesn't involve it.
-/
def foo : Nat Unit
| 0 => ()
| n+1 => foo n
-- Second recursive function with same name.
/-
def foo : Nat → Unit
| 0 => ()
| n+1 => foo n
-/
-- error: equation compiler failed to create auxiliary declaration 'foo._main'
-- nested exception message:
-- invalid declaration, a declaration named 'foo._main' has already been declared
/-
[Leo]: Rob Lewis reported the issue for Lean3 a few years ago. I told him I would not fix it since I think it is obvious to understand the problem. We will write a new equation compiler. We will fix it if it only if it doesn't increase the complexity.
-/