Default argument initializer scoping rule change, allowing

things like (defun foo (s : (l (length s))) ...).
Default arguments can be initialized by expressions that
refer to the arguments.

* eval.c (bind_args): By means of a local array, defer the evaluation
of optional argument init forms until the lexical environment,
including all the parameters, is captured. Then valuates the forms
in the array, and set the variable values.

* txr.1: Clarify the new scoping rules.

1 files changed, 19 insertions, 6 deletions

diff --git a/eval.c b/eval.c
index 1cfd76f6..142776fa 100644
--- a/eval.c
+++ b/eval.c
@@ -220,8 +220,11 @@ static val lookup_sym_lisp1(val env, val sym)
 
 static val bind_args(val env, val params, val args, val ctx_form)
 {
+  val opt_init_parm[32];
+  val *oi_parm = &opt_init_parm[0], *oi_end = &opt_init_parm[32], *oi_iter;
   val new_bindings = nil;
   val optargs = nil;
+  val new_env;
 
   for (; args && consp(params); args = cdr(args), params = cdr(params)) {
     val param = car(params);
@@ -259,15 +262,18 @@ static val bind_args(val env, val params, val args, val ctx_form)
       eval_error(ctx_form, lit("~s: too few arguments"), car(ctx_form), nao);
     while (consp(params)) {
       val param = car(params);
-      val val = nil;
       if (param == colon_k)
         goto twocol;
       if (consp(param)) {
-        val = car(cdr(param));
-        param = car(param);
+        if (oi_parm == oi_end)
+          eval_error(ctx_form,
+                     lit("~s: too many optional args with initializers"),
+                     car(ctx_form), nao);
+        new_bindings = acons(car(param), car(cdr(param)), new_bindings);
+        *oi_parm++ = car(new_bindings);
+      } else {
+        new_bindings = acons(param, nil, new_bindings);
       }
-      new_bindings = acons(param, eval(val, env, ctx_form),
-                           new_bindings);
       params = cdr(params);
     }
     if (bindable(params))
@@ -279,7 +285,14 @@ static val bind_args(val env, val params, val args, val ctx_form)
     eval_error(ctx_form, lit("~s: too many arguments"), car(ctx_form), nao);
   }
 
-  return make_env(new_bindings, nil, env);
+  new_env = make_env(new_bindings, nil, env);
+
+  for (oi_iter = &opt_init_parm[0]; oi_iter < oi_parm; oi_iter++) {
+    val initval = eval(cdr(*oi_iter), new_env, ctx_form);
+    rplacd(*oi_iter, initval);
+  }
+
+  return new_env;
 twocol:
   eval_error(ctx_form, lit("~a: multiple colons in parameter list"),
              car(ctx_form), nao);