Debuging Part 2

After having debugged the program, the new program is shown below. I followed a programming pattern with the first program, but that pattern did not the follow the algorithm I had in mind. What I wanted to do was to print the first letter encountered in the list. the previous program printed the last letter. It is interested how debugging to bring that out. And I used the helper function called compress.2.run with two inputs to solve. The technique is worth remembering. I think this is related to another technique of scanning the list twice(ie simumlation of 2 for loops, more on that later). 


to compress.2.run :list :item 
 ifelse emptyp :list  
  [output :list]
  [ifelse equalp :item first :list
   [output compress.2.run butfirst :list :item]
   [output sentence first :list compress.2.run butfirst :list first :list]]
end 

to compress.2 :list 
 output compress.2.run :list []
end 

show compress.2 [a a a a b c c a a d d e e e e]

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