Rebol Programming/forskip

USAGE: FORSKIP 'word skip-num body DESCRIPTION: Evaluates a block for periodic values in a series. FORSKIP is a function value. ARGUMENTS word -- Word set to each position in series and changed as a result (Type: word) skip-num -- Number of values to skip each time (Type: integer) body -- Block to evaluate each time (Type: block) (SPECIAL ATTRIBUTES) throw catch SOURCE CODE forskip: func [ "Evaluates a block for periodic values in a series." [throw catch] 'word [word!] {Word set to each position in series and changed as a result} skip-num [integer!] "Number of values to skip each time" body [block!] "Block to evaluate each time" /local orig result ][ if not positive? skip-num [throw make error! join [script invalid-arg] skip-num] if not any [ series? get word port? get word ] [throw make error! {forskip/forall expected word argument to refer to a series or port!}] orig: get word while [any [not tail? get word (set word orig false)]] [ set/any 'result do body set word skip get word skip-num get/any 'result ] ]