[r6rs-discuss] [Formal] asymmetry between fold-left and fold-right

[John Cowan]

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
We want more school houses and less jails; more books and less arsenals;
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the opportunities to cultivate our better natures.  --Samuel Gompers