10 lines
915 B
Rexx
10 lines
915 B
Rexx
/*REXX pgm generates/displays the 'start ──► end' elements of the Van Eck sequence.*/
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parse arg LO HI $ . /*obtain optional arguments from the CL*/
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if LO=='' | LO=="," then LO= 1 /*Not specified? Then use the default.*/
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if HI=='' | HI=="," then HI= 10 /* " " " " " " */
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if $=='' | $=="," then $= 0 /* " " " " " " */
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$$=; z= $ /*$$: old seq: $: initial value of seq*/
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do HI-1; z= wordpos( reverse(z), reverse($$) ); $$= $; $= $ z
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end /*HI-1*/ /*REVERSE allows backwards search in $.*/
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/*stick a fork in it, we're all done. */
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say 'terms ' LO " through " HI ' of the Van Eck sequence are: ' subword($,LO,HI-LO+1)
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