Rebol Programming/for

USAGE: FOR 'word start end bump body DESCRIPTION: Repeats a block over a range of values. FOR is a function value. ARGUMENTS word -- Variable to hold current value (Type: word) start -- Starting value (Type: number series money time date char) end -- Ending value (Type: number series money time date char) bump -- Amount to skip each time (Type: number money time char) body -- Block to evaluate (Type: block) (SPECIAL ATTRIBUTES) catch throw SOURCE CODE for: func [ "Repeats a block over a range of values." [catch throw] 'word [word!] "Variable to hold current value" start [number! series! money! time! date! char!] "Starting value" end [number! series! money! time! date! char!] "Ending value" bump [number! money! time! char!] "Amount to skip each time" body [block!] "Block to evaluate" /local result do-body op ][ if (type? start) <> (type? end) [ throw make error! reduce ['script 'expect-arg 'for 'end type? start] ] do-body: func reduce [[throw] word] body op: :greater-or-equal? either series? start [ if not same? head start head end [ throw make error! reduce ['script 'invalid-arg end] ] if (negative? bump) [op: :lesser?] while [op index? end index? start] [ set/any 'result do-body start start: skip start bump ] if (negative? bump) [set/any 'result do-body start] ] [ if (negative? bump) [op: :lesser-or-equal?] while [op end start] [ set/any 'result do-body start start: start + bump ] ] get/any 'result ]