Allow braced output variables to actually be arbitrary substitutions.

* eval.c (subst_vars): Treat the variable as an arbitrary
expression rather than just a symbol.

* match.c (subst_vars): Likewise.

* parser.y (o_var): Further simplification. The first item in
an output var is an expr and not an IDENT.

* txr.1: Updated.

* txr.vim: Likewise.

1 files changed, 17 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 79943997..98a1387a 100644
--- a/txr.1
+++ b/txr.1
@@ -3334,6 +3334,8 @@ for the output clause. The syntax for this is @(NAME :filter <filterspec>}.
 The filter specification syntax is the same as in the output clause.
 See Output Filtering below.
 
+.SS Output Variables: Indexing
+
 Additional syntax is supported in output variables that is does not appear
 in pattern matching variables.
 
@@ -3367,6 +3369,21 @@ The above produces the text "b,c" in a field 10 spaces wide. The [1..3]
 argument extracts a range of a; the "," argument specifies an alternate
 separator string, and 10 specifies the field width.
 
+.SS Output Substitutions
+
+The brace syntax has another syntactic and semantic extension. In place
+of the symbol, an expression may appear. The value of that expression
+is substituted.
+
+Example:
+
+ @(bind a "foo")
+ @(output)
+ @{`@a:` -10}
+
+Here, the quasiliteral expression `@a:` is evaluated, producing the string
+"foo:". This string is printed right-adjusted in a 10 character field.
+
 .SS The Repeat Directive
 
 The repeat directive is generates repeated text from a ``boilerplate'',