ljdickey@watmath.waterloo.edu (L.J.Dickey) (06/11/91)
In article <ROCKWELL.91Jun6222025@socrates.umd.edu> rockwell@socrates.umd.edu (Raul Rockwell) writes: >I used f :'' and f@] in my last post ... Along the same vein, comparing features in J: The adverb "~" (double) has the effect of causing a monadic function call to be treated dyadically by doubling the right argument: f~ x <--> x f x This is nice for building tables, for instance, as in +/ ~ i. 4 because you don't have to type the "i. 4" twice, and sometimes it cuts down on the need for parentheses (compare (i. 4) +/ i. 4 for example). Now, to get to my point. Double can be simulated by the hook. Consider any function f, and compare f ~ x f ] x To take a specific example, consider these three function. pr =. +% f1 =. pr ~ f2 =. pr ] Then f1 4 5 4.25 5.2 f2 4 5 4.25 5.2 Showing that the hook (used in f2) produces the same result as the double (used in f1). Of course the functions f1 and f1 are not identical, since dyadic usages are different, as in 4 f1 5 5.25 4 f2 5 4.2 -- Prof L.J. Dickey, Faculty of Mathematics, U of Waterloo, Canada N2L 3G1 internet: ljdickey@watmath.UWaterloo.ca BITNET/EARN: ljdickey@watdcs obsolescent?: ljdickey@watmath.waterloo.edu UUCP: ljdickey@watmath.UUCP ..!uunet!watmath!ljdickey