txr: support variable in postive match.

In the @{var mod} syntax in the pattern language, allow mod to
be a variable which contains a regex or integer, not just an
integer or regex literal.

* match.c (h_var): Check for modifier being a variable, and
resolve it.

* parser.y (modifiers): Allow a SYMTOK phrase.

* txr.1: Documented.

1 files changed, 21 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 7d6e00bb..206cdd16 100644
--- a/txr.1
+++ b/txr.1
@@ -2179,6 +2179,7 @@ enclosed with the variable in braces:
 .mets >> @{ bident <> / regex /}
 .mets >> @{ bident >> ( fun >> [args ...])}
 .mets >> @{ bident << number }
+.mets >> @{ bident << bident }
 .cble
 
 These specify a variable binding that is driven by a positive match derived
@@ -2227,6 +2228,26 @@ This syntax is processed without consideration of what other
 syntax follows.  A positive match may be directly followed by an unbound
 variable.
 
+The
+.cblk
+.mets >> @{ bident << bident }
+.cble
+syntax allows the
+.meta number
+or
+.meta regex
+modifier to come from a variable. The variable must be bound and contain
+a non-negative integer or regular expression.
+For example,
+.code "@{x y}"
+behaves like
+.code "@{x 3}"
+if
+.code y
+is bound to the integer 3. It is an error if
+.code y
+is unbound.
+
 .coSS Special Symbols @ nil and @ t
 
 Just like in the Common Lisp language, the names