New: length-list-<, length-<

These are functions for testing whether a list or
sequence is shorter than a given integer. This is cheaper
than calculating the length of lists, which is in
some cases impossible if they are infinite.

A length-str-< function already exists, useful
with lazy strings.

length-< uses length-list-< or length-str-<
as appropriate

* lib.[ch] (length_list_lt, length_lt): New functions.

* eval.c (eval_init): length-list-< and length-<
intrinsics registered.

* tests/012/seq.tl: New tests.

* txr.1: Documented.

1 files changed, 2 insertions, 0 deletions

diff --git a/eval.c b/eval.c
index d5cc61c8..42a7d67f 100644
--- a/eval.c
+++ b/eval.c
@@ -7280,6 +7280,7 @@ void eval_init(void)
     reg_fun(intern(lit("proper-list-p"), user_package), proper_list_p_f);
   }
   reg_fun(intern(lit("length-list"), user_package), func_n1(length_list));
+  reg_fun(intern(lit("length-list-<"), user_package), func_n2(length_list_lt));
 
   reg_fun(intern(lit("mapcar"), user_package), func_n1v(mapcarv));
   reg_fun(intern(lit("mapcar*"), user_package), func_n1v(lazy_mapcarv));
@@ -7739,6 +7740,7 @@ void eval_init(void)
   reg_fun(intern(lit("str-seq"), user_package), func_n1(str_seq));
   reg_fun(intern(lit("length"), user_package), length_f);
   reg_fun(intern(lit("len"), user_package), length_f);
+  reg_fun(intern(lit("length-<"), user_package), func_n2(length_lt));
   reg_fun(intern(lit("empty"), user_package), func_n1(empty));
   reg_fun(intern(lit("copy"), user_package), func_n1(copy));
   reg_fun(intern(lit("sub"), user_package), func_n3o(sub, 1));