TXR quasiliterals and output vars treated as Lisp.

* eval.c (format_field): Function moved here from match.c,
along with the introduction of a new behavior: if a meta-expr
occurs among the modifiers, its constituent expression
is evaluated in its place. This allows for @{a @[expr]}
which was previously not allowed in Lisp quasiliterals,
but worked in TXR quasiliterals due to the treatment
of @ by txeval.
(subst_vars): Static function turns external, so code in
match.c can call it instead of the subst_vars in that module.
For that purpose, it needs to take a filter argument and
process filters, like the match.c subst_vars.
(op_quasi_lit): Pass nil as filter argument to subst_vars.

* eval.h (format_field, subst_vars): Declared.

* match.c (format_field): Function removed, moved to
eval.c and slightly changed.
(subst_vars): Renamed to tx_subst_vars. By default, now just a
wrapper for subst_vars. In compatibility mode, invokes the
old logic.
(do_txeval, do_output_line): Call tx_subst_vars rather than
subst_vars.

* match.h (format_field): Declaration removed.

* parser.y (expr): Grammar production removed: no longer
referenced.
(o_var): Braced variable case now parsed as n_expr, and
expanded as expr by default, since this is Lisp now. In
compatibility mode, expanded using expand_meta.
Also SYMTOK case must be subject to expansion; an output
var can now be a symbol macro.
(expand_meta): Expand a quasi-literal as Lisp, except
in compatibility mode.

* txr.1: Bit of a documentation update. Existing doc isn't
totally clear.

1 files changed, 8 insertions, 2 deletions

diff --git a/txr.1 b/txr.1
index 003ace07..19b9f58d 100644
--- a/txr.1
+++ b/txr.1
@@ -2555,8 +2555,7 @@ escape for encoding a literal
 .code @
 character.  Quasiliterals support the full output variable
 syntax. Expressions within variables substitutions follow the evaluation rules
-of \*(TL when the quasiliteral occurs in \*(TL, and the rules of
-the \*(TX pattern language when the quasiliteral occurs in the pattern language.
+of \*(TL.  This hasn't always been the case: see the COMPATIBILITY section.
 
 Quasiliterals can be split into multiple lines in the same way as ordinary
 string literals.
@@ -38863,6 +38862,13 @@ of these version values, the described behaviors are provided if
 is given an argument which is equal or lower. For instance
 .code -C 103
 selects the behaviors described below for version 105, but not those for 102.
+.IP 128
+Compatibility with \*(TX 128 or earlier brings back the behavior that
+expressions in quasiliterals are evaluated according to \*(TX evaluation
+rules for quasiliterals which occur in the \*(TX pattern language.
+Similarly, expressions in
+.code @(output)
+blocks are treated \*(TX pattern language expressions.
 .IP 127
 In versions of \*(TX until 127, the functions
 .codn symbol-function ,