> BTW, when you say it has a cost -- any idea how big that cost is? Would be helpful to guide me in the future...

I assumed this was well known. Kinda glad it's not because I'm including a bit about it in my talk :) I'll add benchmarks - it's actually pretty interesting. blocks are faster for arrays up to around 70 elements, then it sorta breaks even up to 100, then lambdas are faster :) Most of the arrays we're using are smaller than 70 elements (more like 2 to 10) so there's value in yielding instead of passing the block.