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From: soo <tilde@xxxxxxxxxxx> Subject: Re: a preface Date: 25 Mar 2004 21:33:24 +0900 > * From: David Van Horn <dvanhorn@xxxxxxxxxx> > >> | Why does fmt have two very distinct behaviors? > > Because the required optional arguments are different according to the type. > > >> | Why not have two distinct > >> | procedures? > > Why must have two procedure? Inspite of the same processing course and return > type(string). I can think of one reason for not overloading the function. Suppose I like to write a procedure that takes a list of objects, and print out each element per line, left-padded to 20 columns, using 'write' representation. (defun (foo list-of-objects) (for-each (cut fmt <> 20 write "\n") list-of-objects)) Oops, this fails if list-of-objects contains numeric values, right? I think I suppose to write something like this: (defun (foo list-of-objects) (for-each (lambda (elt) (if (number? elt) (fmt elt 20 "\n") (fmt elt 20 write "\n"))) list-of-objects)) However, I think this is awkward. The trouble is, only the programmer knows how she wants to treat a given object as a numeric value or as just "one of Scheme values"---the program can't deduct the programmer's intention purely from the type of the object. Having two distinct procedures at least help a programmer to express the intention. --shiro