24 lines
968 B
Rexx
24 lines
968 B
Rexx
/*REXX pgm generates/displays the 'start --> end' elements of the Van Eck sequence.*/
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Parse Arg lo hi d . /*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 d=='' | d==',' Then d= 0 /* " " " " " " */
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dd=''
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z=d /*dd: old seq: d: initial value of seq*/
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Do i=1 To hi-1
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za=wordpos(reverse(z),reverse(dd))
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zb=0
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wdd=words(dd)
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Do zz=wdd To 1 By -1
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If z=word(dd,zz) Then Do
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zb=wdd-zz+1
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Leave
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End
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End
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z=za
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dd=d
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d=d z
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End /*HI-1*/ /*REVERSE allows backwards search in d.*/
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Say 'terms ' lo ' through ' hi ' of the Van Eck sequence are: ' subword(d,lo,hi-lo+1)
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Exit
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/*stick a fork in it, we're all done. */
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