utils: Add alist-pick.

* shroud/utils.scm (alist-pick): New procedure.

1 files changed, 11 insertions, 0 deletions

diff --git a/shroud/utils.scm b/shroud/utils.scm
index 20545e1..59dbbc2 100644
--- a/shroud/utils.scm
+++ b/shroud/utils.scm
@@ -24,6 +24,7 @@
             vhash-replace
             vhash-values
             alist-compact
+            alist-pick
             gpg-binary
             call-with-encrypted-output-file
             call-with-decrypted-input-file))
@@ -58,6 +59,16 @@ such key."
            (loop tail (cons key keys)
                  (alist-cons key value result)))))))
 
+(define (alist-pick alist key)
+  "Return a list of the values in ALIST that are associated with KEY."
+  (fold-right (lambda (key+value result)
+          (match key+value
+            ((k . value)
+             (if (equal? key k)
+                 (cons value result)
+                 result))))
+        '()  alist))
+
 (define gpg-binary (make-parameter "gpg"))
 
 (define (call-with-pipe* program+args mode proc)