narg: new variaexpand macro.

1 files changed, 36 insertions, 0 deletions

diff --git a/cppawk-narg.1 b/cppawk-narg.1
index 3c1d8a3..bd6c60e 100644
--- a/cppawk-narg.1
+++ b/cppawk-narg.1
@@ -12,6 +12,7 @@
   #define splice(\fIargs\fP)
   #define varexpand(\fIfirst_mac\fP, \fIrest_mac\fP, ...)
   #define variexpand(\fIfirst_mac\fP, \fIrest_mac\fP, ...)
+  #define variaexpand(\fIfirst_mac\fP, \fIrest_mac\fP, \fIarg\fP, ...)
   #define revarg(...)
 .ft R
 
@@ -390,6 +391,41 @@ it with
 .B __LINE__
 and a prefix to generate unique variables.
 
+.IP \fBvariaexpand\fB
+One more macro in the
+.B varexpand
+family is
+.BR variaexpand .
+
+Like
+.BR variexpand ,
+.B variaexpand
+also passes the argument number to its child clauses.
+In addition to the argument number, it passes one more argument:
+a fixed argument specified in the
+.B variexpand
+invocation.
+
+For instance, suppose we wish to have a macro with the following properties:
+
+.ft B
+  series(\fIm\fP, \fIa\fP) \fI->\fP \fIm\fP(\fIa1\fP)
+  series(\fIm\fP, \fIa\fP, \fIb\fP) \fI->\fP \fIm\fP(\fIa1\fP) + \fIm\fP(\fIb2\fP)
+  series(\fIm\fP, \fIa\fP, \fIb\fP, \fIc\fP) \fI->\fP \fIm\fP(\fIa1\fP) + \fIm\fP(\fIb2\fP) + \fIm\fP(\fIc3\fP)
+.ft R
+
+In our expansion, we want the argument numbers to be put into correspondence
+with the arguments, and the argument
+.B x
+to be distributed into the terms:
+
+.ft B
+  #define series_first(\fIx\fP, \fIi\fP, \fIa\fP) \fIa\fP(\fIx\fP ## \fIi\fP)
+  #define series_next(\fIprev\fP, \fIx\fP, \fIi\fP, \fIa\fP) \fIprev\fP + \fIa\fP(\fIx\fP ## \fIi\fP)
+  #define series(\fIa\fP, ...) variaexpand(\fIseries_first\fP, \fIseries_next\fP, \e
+                                     \fIa\fP, __VA_ARGS__)
+.ft R
+
 .SH BUGS
 As noted in the DESCRIPTION, the
 .BR narg ,