bug#55676: [PATCH] non-recursive Lisp reader

[Mattias Engdegård]

You probably saw this one coming. It's a restructuring of the Lisp reader so 
that it no longer uses recursion for reading nested data structures.

The primary motivation is eliminating the limitation of the C stack (and 
potential overflow crash). As a happy side-effect, the change improves reader 
performance by a few percent, exact amount depending on what is being read. 
This translates into a small but measurable speed-up in loading packages (.el 
and .elc), and in byte-compilation. The performance increase is both from 
removal of recursion and closer attention to performance.

Care has been taken to not change the reader behaviour, although some error 
handling may differ in unimportant ways. Some obvious bugs found during the 
conversion have been fixed: for example, #_ followed by whitespace now 
represents the interned empty symbol; previously, it gave an unintended empty 
symbol. A non-breaking space after a single dot now results in the dot token 
instead of the dot as a symbol.

lread-nonrec.diff
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