Allow t symbol in macro parameter lists.

* eval.c (expand_params_rec, bind_macro_params): Handle t
specially everywhere a parameter can occur. Expansion
allows the syntax through without extending the
environment with a t variable; binding walks over
the structure without binding a variable.

* stdlib/compiler.tl (expand-bind-mac-params): Likewise,
handle occurrences of t, suppressing the generation of
and assignment to variables, while ensuring that
initializing expressions are evaluated.

* tests/011/tree-bind.tl: New file.

* txr.1: Documented.

1 files changed, 20 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 66016541..7be5a547 100644
--- a/txr.1
+++ b/txr.1
@@ -39715,6 +39715,21 @@ and
 .codn "(d e)" .
 These compounds express nested macro parameter lists.
 
+Starting in \*(TX 285, the symbol
+.code t
+can be used in a macro parameter list in place of a parameter name.
+This indicates that an object is expected at that position in the
+corresponding structure, but no variable will be bound.
+For completeness, the
+.code t
+symbol may also be used for a presence-indicating variable.
+When the name of an optional parameter is specified as
+.codn t ,
+and the corresponding structure is missing, the
+.meta init-val
+expression, if present, is still evaluated under the same
+circumstances as it would if a variable were present.
+
 Nested macro parameter lists recursively match the corresponding structure
 in the argument object.  For instance if a simple argument would capture
 the structure
@@ -39846,6 +39861,11 @@ and binds to the entire
 .code tree-bind
 form.
 
+ANSI CL doesn't support the convention that the
+.code t
+symbol may appear instead of a parameter symbol to
+suppress the binding of a variable.
+
 .NP* The Macro Expansion Process
 
 The following description omits the treatment of top-level forms by