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| author | Kaz Kylheku <kaz@kylheku.com> | 2023-10-05 14:56:33 -0700 |
|---|---|---|
| committer | Kaz Kylheku <kaz@kylheku.com> | 2023-10-05 14:56:33 -0700 |
| commit | 1a8ca97932bc4c923ba7d5f2ae27b2bf754884b8 (patch) | |
| tree | 6a9c0cb0f36a4a422140359123abed5be407fbdd /lib.c | |
| parent | 3b87081903c42cdfe0eaf58629b90a83351b7a87 (diff) | |
| download | txr-1a8ca97932bc4c923ba7d5f2ae27b2bf754884b8.tar.gz txr-1a8ca97932bc4c923ba7d5f2ae27b2bf754884b8.tar.bz2 txr-1a8ca97932bc4c923ba7d5f2ae27b2bf754884b8.zip | |
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.
Diffstat (limited to 'lib.c')
| -rw-r--r-- | lib.c | 28 |
1 files changed, 28 insertions, 0 deletions
@@ -4857,6 +4857,19 @@ val length_list(val list) return bn_len; } +val length_list_lt(val list, val len) +{ + val self = lit("length-list-lt"); + cnum le = c_num(len, self); + + while (consp(list) && le > 0) { + list = cdr(list); + le--; + } + + return tnil(le > 0); +} + static val length_proper_list(val list) { cnum len = 0; @@ -13147,6 +13160,21 @@ val length(val seq) } } +val length_lt(val seq, val len) +{ + switch (type(seq)) { + case NIL: + return if3(plusp(len), t, nil); + case CONS: + case LCONS: + return length_list_lt(seq, len); + case LSTR: + return length_str_lt(seq, len); + default: + return lt(length(seq), len); + } +} + val sub(val seq, val from, val to) { switch (type(seq)) { |