diff options
| -rw-r--r-- | guix/profiles.scm | 27 |
1 files changed, 20 insertions, 7 deletions
diff --git a/guix/profiles.scm b/guix/profiles.scm index 793af2463f..2742ba8933 100644 --- a/guix/profiles.scm +++ b/guix/profiles.scm @@ -80,6 +80,7 @@ generation-number generation-numbers profile-generations + relative-generation previous-generation-number generation-time generation-file-name)) @@ -503,16 +504,28 @@ former profiles were found." '() generations))) -(define (previous-generation-number profile number) +(define* (relative-generation profile shift #:optional + (current (generation-number profile))) + "Return PROFILE's generation shifted from the CURRENT generation by SHIFT. +SHIFT is a positive or negative number. +Return #f if there is no such generation." + (let* ((abs-shift (abs shift)) + (numbers (profile-generations profile)) + (from-current (memq current + (if (negative? shift) + (reverse numbers) + numbers)))) + (and from-current + (< abs-shift (length from-current)) + (list-ref from-current abs-shift)))) + +(define* (previous-generation-number profile #:optional + (number (generation-number profile))) "Return the number of the generation before generation NUMBER of PROFILE, or 0 if none exists. It could be NUMBER - 1, but it's not the case when generations have been deleted (there are \"holes\")." - (fold (lambda (candidate highest) - (if (and (< candidate number) (> candidate highest)) - candidate - highest)) - 0 - (generation-numbers profile))) + (or (relative-generation profile -1 number) + 0)) (define (generation-file-name profile generation) "Return the file name for PROFILE's GENERATION." |