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The orders egg provides functions useful for defining orders for sorting.
There's no documentation about it right now. Sorry. :-(
[procedure] (cmp-key cmp key)
Generates an ordering procedure that applies the 'key' proc to both sort candidates, and compares the resulting keys using the 'cmp' procedure.
E.g. to sort a list of integers based on their value modulo-10: (sort my-numbers (cmp-key < (cut modulo <> 10)))
[procedure] (key-string< key)
Generates an ordering procedure (see cmp-key) that sorts strings using string< (defined in SRFI-13).