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utils: Add take-up-to.

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* haunt/utils.scm (take-up-to): New procedure.
This commit is contained in:
David Thompson
2015-04-11 22:26:44 -04:00
parent 35bb74497d
commit c2191a68f2
1 changed files with 11 additions and 0 deletions
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11
haunt/utils.scm
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@@ -36,6 +36,7 @@
clean-directory clean-directory
mkdir-p mkdir-p
string->date* string->date*
take-up-to))
(define* (flatten lst #:optional depth) (define* (flatten lst #:optional depth)
"Return a list that recursively concatenates the sub-lists of LST, "Return a list that recursively concatenates the sub-lists of LST,
@@ -105,3 +106,13 @@ flattened."
"Convert STR, a string in '~Y~m~d ~H:~M' format, into a SRFI-19 date "Convert STR, a string in '~Y~m~d ~H:~M' format, into a SRFI-19 date
object." object."
(string->date str "~Y~m~d ~H:~M")) (string->date str "~Y~m~d ~H:~M"))
(define (take-up-to n lst)
"Return the first N elements of LST or an equivalent list if there
are fewer than N elements."
(if (zero? n)
'()
(match lst
(() '())
((head . tail)
(cons head (take-up-to (1- n) tail))))))