[Greg Wilson]
> I would also like to volunteer to repeat the "simultaneous loop" syntax
> experiment with list comprehensions, i.e. see whether what's being
> proposed lines up with people's pre-existing intuitions.
[Guido]
> Please do!
>
> Though I have no doubt of the outcome:
>
> [x+y for x in [10, 20, 30] for y in [1, 2, 3]]
>
> will be almost universally understood to mean
>
> [11, 12, 13, 21, 22, 23, 31, 32, 33].
I'm not sure about that! Greg hangs out with functional programmers and old
Fortran-heads. Fortran has a handy construct called "implied DO (loops)" in
I/O statements, and in those the *innermost* (leftmost) shorthand loop
varies fastest. So I expect the Fortran'ers to guess
[11, 21, 31, 12, 22, ...]
I agree the experiment is worth trying, but I'm not sure we're observing
anything other than experienced programmers' prior language-dependent
conditioning ... which would also explain why neither Greg's functional nor
Fortran guinea pigs had any concept of lockstep iteration across multiple
loop controls.
BTW, an MxN slice of a 2D array A in Fortran will often show up in an I/O
stmt as
... ((A(I,J), I=1,M), J=1,N) ...
and the "innermost fastest" rule relates directly to Fortran's oddball
decision to use column-major array storage: the natural way to write the
I/O using implied DOs caters to varying the first index fastest (==
contiguous memory locations under column-major storage). It's not like
there's a *profound* reason behind this <wink>.
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