binding rules

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Author Thread:

j.merrill

binding rules
Posted: Friday, July 15, 2005 10:12 AM (EST)

For those reading this thread, paste Nicolai's code into APL to see what it really looks like. (The rendition in the browser that I see is quite silly. Part of the problem is that the font is so small that the brackets look like stile chars.)

Those are not equivalent (as you can see from the error in one case and not the other). The text

   1 2 3

is a constant (numeric) vector, just like the expression

    'ABC'

is a constant vector (this time character).  The text

    A B C

is an expression. An expression cannot be indexed (or assigned) unless it is parenthesized.



William.Rutiser

binding rules
Posted: Friday, July 15, 2005 11:05 AM (EST)

EVOLUTION ERROR is given in several awkward cases where the STSC and IBM APL definitions once diverged. In this case, it has to do with the left scope of the indexing brackets. One arguable definition would treat A B C[2] as A B (C[2]) while another would treat it as ( A B C )[2]. This error was added to trap old code that depends on either definition. Add a pair of parens to make your intent clear to the interpreter as well as other programmers.