OpenEuphoria

1. foldl, foldr

• Posted by bill Oct 11, 2011
• 34476 views

Jeremy raised an issue about foldl, foldr (and by extenstion zip, zip2, map, iterate,... functional extensions of Euphoria - Dec 2010).

Consider:

function add(atom X, atom a) return X+a  end function 
function minus(atom X, atom a) return X-a  end function 
function max(atom X, atom a)  
  if X >= a then return X end if  
  return a  
end function 
 
constant ADD = routine_id("add") 
constant MINUS = routine_id("minus") 
constant MAX = routine_id("max") 
 
function foldl(sequence S, integer op, atom acc) 
  atom ACC = acc 
  for i = 1 to length(S) do 
    ACC = call_func(op,{ACC,S[i]}) 
  end for 
  return ACC 
end function 
 
? foldl({1,2,3,4,5,6,7,8,9}, ADD, 0) 
printf(1,"------------------\n") 
? foldl({1,-2,3,-4,5,-6,7,-8,9,-10,11}, MINUS, 0) 
printf(1,"------------------\n") 
? foldl({1,-2,3,-4,5,-6,7,-8,9,-10,11}, MAX, 0) 
printf(1,"------------------\n") 

Of course we could use a macro to replace the framework so we would be saying:

foldl(S,+,0) effectively.