Courses/CS 460/Fall 2005/Homework/Kelly Breed/Oct 15

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Contents 1 HW 3 1.1 Member 1.2 Last 1.3 Nth 1.4 Length 1.5 Permute

[edit] HW 3

[edit] Member

This returns true on finding a match against a list.

local
   proc {Member L M ?O}
      H T in
      choice
	 L=nil fail
      [] L=H|T H=M O=true
      [] L=H|T {Member T M O}
      end
   end
   
in
{Browse {SearchAll fun {$} {Member ['one' 'two' 'three' 'four'] 'three'} end }}
end

[edit] Last

Returns the last element of a list.

local
   proc {Last I ?Out}
      H T in
      choice
	 I = nil fail
      [] I=H|nil Out=H
      [] I=_|T {Last T Out}
      end
   end

in
   {Browse {SearchAll fun {$} {Last [2 4 5 8 6]} end}}
end

[edit] Nth

Returns the Nth element of a list.

local
   proc {Nth L I S ?Out}
      H T in
      choice
	 L=nil fail
      [] L=H|T S=I Out=H
      [] L=_|T {Nth T I S+1 Out}
      end
   end
in
   {Browse {SearchAll fun {$} {Nth [7 5 3 8 9] 4 1} end }}
end

[edit] Length

Returns the length of a list.

local
   proc {Length I S ?Out}
      H T in
      choice
	 I=nil fail
      [] I=H|nil Out=S
      [] I=_|T {Length T S+1 Out}
      end
   end
in
   {Browse {SearchAll fun {$} {Length [a b c d e] 1} end}}
end

[edit] Permute

local
    proc {Delete L M ?Out}
      H T in
      L=H|T
      choice
	 M=H
	 Out=T
      [] Out=H|{Delete T M}
      end
    end
    
   proc {Permute L ?Out}
      Element  Rest in
      choice
	 L=nil
	 Out=nil
      [] 
	 Rest = {Delete L Element}
	 Out = Element|{Permute Rest}
      end
   end
in
{Browse {SearchAll fun {$} {Permute [a b c d]} end}}
end

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