diff options
-rw-r--r-- | builtin.c | 4 | ||||
-rw-r--r-- | docs/content/3.manual/manual.yml | 18 | ||||
-rw-r--r-- | tests/all.test | 4 |
3 files changed, 26 insertions, 0 deletions
@@ -1090,6 +1090,10 @@ static const char* const jq_builtins[] = { " def _while: " " if cond then ., (update | _while) else empty end; " " try _while catch if .==\"break\" then empty else . end;", + "def until(cond; next): " + " def _until: " + " if cond then . else (next|_until) end;" + " _until;", "def limit($n; exp): if $n < 0 then exp else foreach exp as $item ([$n, null]; if .[0] < 1 then break else [.[0] -1, $item] end; .[1]) end;", "def first(g): foreach g as $item ([false, null]; if .[0]==true then break else [true, $item] end; .[1]);", "def last(g): reduce g as $item (null; $item);", diff --git a/docs/content/3.manual/manual.yml b/docs/content/3.manual/manual.yml index ea0514ed..42c6c98c 100644 --- a/docs/content/3.manual/manual.yml +++ b/docs/content/3.manual/manual.yml @@ -1270,6 +1270,24 @@ sections: input: '1' output: ['[1,2,4,8,16,32,64]'] + - title: "`until(cond; next)`" + body: | + + The `until(cond; next)` function allows you to repeatedly + apply the expression `next`, initially to `.` then to its own + output, until `cond` is true. For example, this can be used + to implement a factorial function (see below). + + Note that `until(cond; next)` is internally defined as a + recursive jq function. Recursive calls within `until()` will + not consume additional memory if `next` produces at most one + output for each input. See advanced topics below. + + examples: + - program: '[.,1]|until(.[0] < 1; [.[0] - 1, .[1] * .[0]])|.[1]' + input: '4' + output: ['24'] + - title: "`recurse(f)`, `recurse`, `recurse(f; condition)`, `recurse_down`" body: | diff --git a/tests/all.test b/tests/all.test index c4c3b0df..8d27d331 100644 --- a/tests/all.test +++ b/tests/all.test @@ -250,6 +250,10 @@ null 1 [1,2,4,8] +[.[]|[.,1]|until(.[0] < 1; [.[0] - 1, .[1] * .[0]])|.[1]] +[1,2,3,4,5] +[1,2,6,24,120] + [foreach .[] as $item ([3, null]; if .[0] < 1 then break else [.[0] -1, $item] end; .[1])] [11,22,33,44,55,66,77,88,99] [11,22,33] |