.macro for :for.values :for.instr ~
   [:for.var first :for.values] ~
   [:for.initial run first bf :for.values] ~
   [:for.final run first bf bf :for.values] ~
   [:for.step forstep] ~
   [:for.tester (ifelse :for.step < 0 ~
                        [[:for.initial < :for.final]] ~
                        [[:for.initial > :for.final]])]
local :for.var
catch "for.catchtag [op for.done runresult [forloop :for.initial]]
op []
end

to forloop :for.initial
make :for.var :for.initial
if run :for.tester [throw "for.catchtag]
run :for.instr
.maybeoutput forloop (:for.initial + :for.step)
end

to for.done :for.result
if emptyp :for.result [op [stop]]
op list "output quoted first :for.result
end

to forstep
if equalp count :for.values 4 [op run last :for.values]
op ifelse :for.initial > :for.final [-1] [1]
end

bury [for forstep forloop for.done]