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jlang-operations.txt
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jlang-operations.txt
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J Language Operations
=====================
The J language is one of the main descendents of APL, and as such
embodies a large amount of knowledge about array programming. It is
this author's opinion that any serious array programming system should
be able to express all of the concepts and operators in J.
While simply doing a feature-wise comparison might satisfy many that
this is the case, I think a better approach would be to write a J
interpreter using the ndarray as its underlying computational
infrastructure.
A first step is to catalog some J primitives, and indicate how
they can correspond to functions and expression graph nodes in the
ndarray system. To do this comparison, I'm using the "J Primer"
on www.jsoftware.com.
Right-associativity
-------------------
Operations in general, and reduction operations in particular,
are right-associative in J. For example, "1 - 2 - 3" means
"1 - (2 - 3)", contrary to the typical mathematical interpretation
of "(1 - 2) - 3".