b2/: meta-variable $ for "previously matched variable"

We need this for iterative processing of FN.

b2/SUBST

@@ -1,5 +1,7 @@
 FN=DNP { ignore }
 
+FN=X(*) { $=$1 }
+
 REF=R[0-9]* {
 	T=R
 	VAL=(#R) { R=$1 }
@@ -23,8 +25,9 @@ variable:
   $foo, ...
 with curly braces:
   ${foo}, ...
-input variable:
+input variable (in pattern):
   $$
+the input variable ($) can also be used as LHS for matches and assignments
 
   Caveat:
 

b2/boom.c

@@ -94,6 +94,7 @@ int main(int argc, char **argv)
 	void (*process)(const char *name) = parse_hierarchy;
 	int i;
 
+	dollar = unique("$");
 	for (i = 1; i != argc; i++) {
 		if (*argv[i] == '-') {
 			if (!strcmp(argv[i], "-c"))

b2/lang.h

@@ -17,6 +17,8 @@
 #include "subst.h"
 
 
+extern const char *dollar; /* "$" */
+
 extern struct action hierarchy;
 extern struct subst *substitutions;
 

b2/lang.y

@@ -25,6 +25,8 @@
 #include "y.tab.h"
 
 
+const char *dollar;
+
 struct action hierarchy;
 struct subst *substitutions = NULL;
 
@@ -110,6 +112,7 @@ static const struct field *top_field(void)
 %type	<stock>		stock
 %type	<prov>		providers provider
 %type	<subst>		substitutions block opt_block
+%type	<s>		word_or_dollar
 
 %%
 
@@ -589,7 +592,7 @@ block:
 		{
 			$$ = NULL;
 		}
-	| WORD relop PATTERN opt_block block
+	| word_or_dollar relop PATTERN opt_block block
 		{
 			if ($4) {
 				if ($2 != rel_eq)
@@ -622,6 +625,17 @@ block:
 		}
 	;
 
+word_or_dollar:
+	'$'
+		{
+			$$ = dollar;
+		}
+	| WORD
+		{
+			$$ = $1;
+		}
+	;
+
 opt_block:
 		{
 			$$ = NULL;

b2/param.h

@@ -66,6 +66,8 @@ struct value {
  * When using "struct param" to store (string) variables not associated to a
  * field, then u.name contains the variable name, "op" contains the relational
  * operator (default rel_eq), and value.u.s contains the variable's value.
+ *
+ * If the variable is "$", then u.name is set to NULL.
  */
 
 struct param {

b2/subex.c

@@ -20,6 +20,7 @@
 
 #include "util.h"
 #include "vstring.h"
+#include "lang.h"
 #include "relop.h"
 #include "subst.h"
 #include "subex.h"
@@ -163,46 +164,53 @@ static int do_match_1(const char *var, const regex_t *re,
 }
 
 
-static int do_match(const char *var, const regex_t *re,
+static int do_match(const char **var, const regex_t *re,
     const struct param *in, const struct param *out,
     const char **val, regmatch_t *match)
 {
 	int i;
 
-	if (var != fn)
-		return do_match_1(var, re, in, out, val, match);
+	if (*var != fn)
+		return do_match_1(*var, re, in, out, val, match);
 	for (i = 0; i != FIELDS; i++)
-		if (!do_match_1(f[i], re, in, out, val, match))
+		if (!do_match_1(f[i], re, in, out, val, match)) {
+			*var = f[i];
 			return 0;
+		}
 	return -1;
 }
 
 
 static const struct subst *recurse_sub(const struct subst *sub,
-    const struct param *in, const char *s, const regmatch_t *match,
-    const char *units, struct param **out)
+    const struct param *in, const char *matched_var, const char *matched_val,
+    const regmatch_t *match, const char *units, struct param **out)
 {
 	const struct subst *jump;
 	regmatch_t m_tmp[10];
-	const char *val;
+	const char *var, *val;
 	char *tmp;
 
 	while (sub) {
 		switch (sub->type) {
 		case st_match:
-			if (do_match(sub->u.match.src, &sub->u.match.re,
+			var = sub->u.match.src;
+			if (var == dollar)
+				var = matched_var;
+			if (do_match(&var, &sub->u.match.re,
 			    in, *out, &val, m_tmp))
 				break;
-			jump = recurse_sub(sub->u.match.block, in, val, m_tmp,
-			    sub->u.match.units, out);
+			jump = recurse_sub(sub->u.match.block, in,
+			    var, val, m_tmp, sub->u.match.units, out);
 			if (jump && jump != sub)
 				return jump;
 			break;
 		case st_assign:
-			tmp = compose(sub->u.assign.pat, in, *out, s, match,
-			    units);
-			do_assign(sub->u.assign.dst, out, sub->u.assign.op,
-			    tmp);
+			tmp = compose(sub->u.assign.pat, in, *out, matched_val,
+			   match, units);
+			var = sub->u.assign.dst;
+			if (var == dollar)
+				var = matched_var;
+			do_assign(var, out, sub->u.assign.op, tmp);
 			break;
 		case st_end:
 			return &jump_end;
@@ -237,5 +245,6 @@ int substitute(const struct subst *sub, const struct param *in,
 		}
 	}
 	*out = NULL;
-	return recurse_sub(sub, in, NULL, NULL, NULL, out) != &jump_ignore;
+	return recurse_sub(sub, in, NULL, NULL, NULL, NULL, out)
+	    != &jump_ignore;
 }

b2/subst.c

@@ -356,10 +356,14 @@ static void recurse_fin(struct subst *sub, const struct parent *parent)
 		sub->prev = prev;
 		switch (sub->type) {
 		case st_match:
+			if (!parent && sub->u.match.src == dollar)
+				yyerror("$ without match");
 			next.sub = sub;
 			recurse_fin(sub->u.match.block, &next);
 			break;
 		case st_assign:
+			if (!parent && sub->u.assign.dst == dollar)
+				yyerror("$ without match");
 			check_chunks(sub->u.assign.pat, parent, prev);
 			break;
 		case st_end: