> On Dec 18, 2015, at 4:35 AM, Al Skipp via swift-evolution
> <[email protected]> wrote:
>
>> On 18 Dec 2015, at 00:19, T.J. Usiyan via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> With a Cartesian Product type [like
>> this](https://github.com/griotspeak/CartesianProduct
>> <https://github.com/griotspeak/CartesianProduct>), the for-in-where syntax
>> actually gets us to list comprehensions. I'll admit that I might not have
>> implemented the best Cartesian Product type possible, but it should
>> illustrate that we have what we need.
>>
>> `for case … in cartProd(cartProd(seq1, seq2), seq3) // An operator for
>> cartProd would make it more pleasing to read.`
>
> That’s impressive work, but it strikes me as quite a difficult undertaking to
> get there. (Is it just me, or are generators and sequences the most scary
> part of Swift?) Also, is it possible to get it working as an expression, or
> is it restricted to a ‘for’ statement? If it can only be performed as a ‘for’
> statement it will still need an external mutable var to be updated outside of
> the loop. It’s fine if you want to just do side-effecty things, like print
> the elements, but I’d consider the ability to return a value to be more
> important.
This is a much simpler cartesian product implementation:
seq1.flatMap { x in seq2.map { (x,$0) } }
or, if you want speed,
seq1.lazy.flatMap { x in seq2.lazy.map { (x,$0) } }
HTH,
-Dave
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