From 6af67b4a8842fd3b949fa5bfb68811f62a521ae2 Mon Sep 17 00:00:00 2001 From: Stefan Monnier Date: Thu, 27 Oct 2016 01:18:16 -0400 Subject: [PATCH] Reduce lread substitutions. * src/lread.c (read1): After reading an object using the "#n=" syntax, if the read object is a cons cell, instead of recursively substituting the placeholder with the new object, mutate the placeholder cons cell itself to have the correct car and cdr values. --- src/lread.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/src/lread.c b/src/lread.c index 263638651db..a6d04ec5af7 100644 --- a/src/lread.c +++ b/src/lread.c @@ -2990,12 +2990,21 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list) tem = read0 (readcharfun); /* Now put it everywhere the placeholder was... */ - Fsubstitute_object_in_subtree (tem, placeholder); + if (CONSP (tem)) + { + Fsetcar (placeholder, XCAR (tem)); + Fsetcdr (placeholder, XCDR (tem)); + return placeholder; + } + else + { + Fsubstitute_object_in_subtree (tem, placeholder); - /* ...and #n# will use the real value from now on. */ - Fsetcdr (cell, tem); + /* ...and #n# will use the real value from now on. */ + Fsetcdr (cell, tem); - return tem; + return tem; + } } /* #n# returns a previously read object. */ -- 2.39.2