awk macro: don't bind *stdout* if :output missing.

* share/txr/stdlib/awk.tl (awk): Bind *stdout* only if
awc.output is not nil; i.e. :output has been specified
(with a non-nil argument).

* txr.1: Revised :output documentation.

1 files changed, 5 insertions, 14 deletions

diff --git a/txr.1 b/txr.1
index 47a4f0aa..96b15fe8 100644
--- a/txr.1
+++ b/txr.1
@@ -37345,24 +37345,15 @@ clause is processed just after the
 clause. It must have exactly one argument, which is an expression
 that evaluates to a string, or else to an output stream.
 If it evaluates to a string, then that string is used as the name
-of a file to open for writing.
-
-If the
-.code :output
-clause is omitted, then the current value of the
-.code *stdout*
-stream is used: the value which that special
-variable has on entry into the code generated by the
-.code awk
-macro.
+of a file to open for writing, and the resulting stream
+is taken in place of that string.
 
 The
 .code :output
-clause has the effect of creating a local binding for the
+clause, if present, has the effect of creating a local binding for the
 .code *stdout*
-special variable within the dynamic scope of the
-.code awk
-macro. This new value of
+special variable.
+This new value of
 .code *stdout*
 is visible to all forms within the macro.
 If a