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Clarify that term rewriting macros are applied recursively (#9305)

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Fixes https://github.com/nim-lang/Nim/issues/9288 fixes https://github.com/nim-lang/Nim/issues/8376 and fixes https://github.com/nim-lang/Nim/issues/2901

(cherry picked from commit 160f8599c6)
This commit is contained in:
Andrea Ferretti
2018-10-11 15:59:14 +02:00
committed by narimiran
parent 8a9680e3a2
commit fde803745e
1 changed files with 6 additions and 0 deletions
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6
doc/manual.rst
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@@ -5965,6 +5965,12 @@ curlies is the pattern to match against. The operators ``*``, ``**``,
notation, so to match verbatim against ``*`` the ordinary function call syntax
needs to be used.
Term rewriting macro are applied recursively, up to a limit. This means that
if the result of a term rewriting macro is eligible for another rewriting,
the compiler will try to perform it, and so on, until no more optimizations
are applicable. To avoid putting the compiler into an infinite loop, there is
a hard limit on how many times a single term rewriting macro can be applied.
Once this limit has been passed, the term rewriting macro will be ignored.
Unfortunately optimizations are hard to get right and even the tiny example
is **wrong**: