read, iread: source location recording now conditional.

Recording of source location info incurs a time and space
penalty. We don't want to impose this on programs which are
just reading large amounts of Lisp data that isn't code.

* eval.c (eval_init): Register lisp-parse and read functions
to the newly introduced nread function rather than lisp_parse.
lisp_parse continues to record source location info
unconditionally.

* parser.c (rec_source_loc_s): New symbol variable.
(parser_common_init): Set the new member of the parser
structure, rec_source_loc, according to the current value of
the special var *rec-source-loc*.
(lisp_parse_impl): New second argument, rlcp_p. If true, it
overrides the rec_source_loc member of the parser structure
to true.
(lisp_parse): Pass true argument to rlcp_p parameter of
lisp_parse_impl, so parsing via lisp_parse always records
source loc info.
(nread): New function.
(iread): Pass true argument to rlcp_p parameter of
lisp_parse_impl, so *rec-source-loc* controls whether source
location info is recorded.
(parse_init): Initilize rec_source_loc_s symbol variable,
and register the *rec-source-loc* special var.

* parser.h (struct parser): New member, rec_source_loc.
(rec_source_loc_s, nread): Declared.

* parser.y (rlcp_parser): New static function. Like rlcp but
does nothing if parser->rec_source_loc is false.
(rlc): New macro.
(grammar): Replace rlcp uses with rlc, which expands to a call
to rlcp_parser.
(rlrec): Do nothing if source loc recording is not enabled in
the parser.
(make_expr, uref_helper): Replace rlcp with rlc. This is
possible because these functions have a parser local
variable that the macro expansion can refer to.
(parse_once): Override rec_source_loc in the parser to 1, so
that source loc info is always recorded when parsing is
invoked through this function.

* txr.1: Documented *rec-source-loc* and added text under
read and iread.

1 files changed, 35 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index f948f155..a90b5a8a 100644
--- a/txr.1
+++ b/txr.1
@@ -43888,6 +43888,16 @@ possibility that the expression will be further extended by means of the dot or
 dotdot operators. An explicit end-of-input signal must be given from the
 terminal to terminate the expression.
 
+The special variable
+.code *rec-source-loc*
+controls whether these functions record source location info similarly to
+.codn load .
+Note: if these functions are used to scan data which is evaluated as Lisp code,
+it may be useful to set
+.code *rec-source-loc*
+true in order to obtain better diagnostics. However, source location recording
+incurs a performance and storage penalty.
+
 .coNP Function @ record-adapter
 .synb
 .mets (record-adapter < regex >> [ stream <> [ include-match ]])
@@ -54616,6 +54626,31 @@ has location info, the expander propagates that info to that form's
 expansion. In some situations, it is useful for a macro or other code
 transformer to perform this action explicitly.
 
+.coNP Special variable *rec-source-loc*
+.desc
+The Boolean special variable
+.code *rec-source-loc*
+controls whether the
+.code read
+and
+.code iread
+functions record source location info. The variable is
+.code nil
+by default, so that these functions do not record source location info.
+If it is true, then these functions record source location info.
+
+Regardless of the value of this variable, source location info is
+recorded for Lisp forms which are read from files or streams under the
+.code load
+function or specified on the \*(TX command line. Source location
+info is also always recorded when reading the \*(TX pattern language syntax.
+
+Note: recording and propagating location info incurs a memory and performance
+penalty.  The individual cons cells and certain other literal objects in the
+structure which emerges from the parser are associated with source location
+info via a global weak hash table.
+
+
 .coNP Function @ macro-ancestor
 .synb
 .mets (macro-ancestor << form )