update

Task/Function-prototype/J/function-prototype.j

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+   NB. j assumes an unknown name f is a verb of infinite rank
+   NB. f has infinite ranks
+   f b. 0
+_ _ _
+
+   NB. The verb g makes a table.
+   g=: f/~
+
+   NB. * has rank 0
+   f=: *
+
+
+   NB. indeed, make a multiplication table
+   f/~ i.5
+0 0 0  0  0
+0 1 2  3  4
+0 2 4  6  8
+0 3 6  9 12
+0 4 8 12 16
+
+   NB. g was defined as if f had infinite rank.
+   g i.5
+0 1 4 9 16
+
+   NB. f is known to have rank 0.
+   g=: f/~
+
+   NB. Now we reproduce the table
+   g i.5
+0 0 0  0  0
+0 1 2  3  4
+0 2 4  6  8
+0 3 6  9 12
+0 4 8 12 16
+
+
+
+   NB. change f to another rank 0 verb
+   f=: +
+
+   NB. and construct an addition table
+   g i.5
+0 1 2 3 4
+1 2 3 4 5
+2 3 4 5 6
+3 4 5 6 7
+4 5 6 7 8
+
+
+   NB. f is multiplication at infinite rank
+   f=: *"_
+
+
+   NB. g, however, has rank 0
+   g i.5
+0 0 0  0  0
+0 1 2  3  4
+0 2 4  6  8
+0 3 6  9 12
+0 4 8 12 16