|Subject:||Re: [Bug-apl] jot dot jot dot?|
|Date:||Mon, 27 Jun 2016 13:37:30 +0200|
|User-agent:||Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Thunderbird/31.4.0|
not sure. First of all, both IBM APL2 and GNU APL return the same result in Alex's example:
5 ∘.∘.+ 9
5 (∘.∘).+ 9
5 ∘.(∘.+) 9
Then the IBM language reference says this (p. 35):
"For example, the function _expression_ +.×/ is a reduction by a +.× inner product
because the × binds as right operand to the array product operator (.), and not as
left operand to the slash operator (/). The + binds as left operand to the dot; then
the resulting product binds to the slash as its left operand.
+.×/ ←→ (+.× )/ not +.(× /)
However, the binding strength resolves the ambiguity in the IBM example only
because / is not a dyadic operator. In Alex's example the operator is dyadic, and one
could either bind the middle ∘ to the left ∘ or the + to the middle ∘ without violating
the binding strengths. In this case I would argue that the "basic APL2 evaluation rule"
should be applied because ∘.+ can be evaluated (yielding a derived function) because all arguments
of . are available before the . and ∘ on the left show up.
What is missing in both the ISO standard and in the APL2 language reference is a
statement about left-to-right or right-to-left associativity of APL operators. I personally
would find it counter-intuitive if functions are evaluated left-to-right while operators are
On 06/27/2016 11:48 AM, Jay Foad wrote:
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