[r6rs-discuss] [Formal] asymmetry between fold-left and fold-right
cowan at ccil.org
Mon Jan 29 01:57:09 EST 2007
Anton van Straaten scripsit:
> Informally and intuitively, the fold-right procedure folds a procedure
> over the elements of a list in right-to-left order, whereas fold-left
> uses left-to-right order.
As a historical note, DTSS Lisp (the first Lisp I ever learned) defined
MINUS as a right-fold: (MINUS 5) = -5, (MINUS 3 4) = 3 - 4, (MINUS 3 4 5)
= (-3) + 4 + (-5). There was no left-folded subtraction function.
John Cowan http://ccil.org/~cowan cowan at ccil.org
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