tprint and -t option: handle infinite list.

Test case: txr -t '(gun "foo")' must run in
constant memory.

* eval.c (tprint): Rewritten to iterate over lists using
open loop rather than mapdo. Classification of the sequence
is done using the new seq_info, as must be for all new
sequence functions.

* txr.c (txr_main): Implementation of -t, -p and -P captures
the result of the expression in a variable whose value is
zapped when it is passed to the function. A gc_hint is added
so that this isn't optimized away. Thus, this code won't hold
on to the original pointer to a lazy, infinite list.

1 files changed, 9 insertions, 3 deletions

diff --git a/txr.c b/txr.c
index cee8ac51..cd774de0 100644
--- a/txr.c
+++ b/txr.c
@@ -858,13 +858,19 @@ int txr_main(int argc, char **argv)
                                                 tprint));
           val args_saved = or2(orig_args, arg_list);
           val args_new;
+          val obj;
 
           reg_varl(self_path_s, lit("cmdline-expr"));
           reg_var(args_s, or2(orig_args, arg_list));
-          pf(eval_intrinsic(lisp_parse(arg, std_error, colon_k,
-                                       lit("cmdline-expr"), colon_k),
-                            make_env(bindings, nil, nil)), std_output);
+
+          obj = eval_intrinsic(lisp_parse(arg, std_error, colon_k,
+                                          lit("cmdline-expr"), colon_k),
+                               make_env(bindings, nil, nil));
+          gc_hint(obj);
+          pf(z(obj), std_output);
+
           evaled = t;
+
           args_new = cdr(lookup_global_var(args_s));
           if (args_new != args_saved) {
             arg_list = args_new;