Ruby do/end vs braces

Question

Why does this map expression produce different results depending on whether I use braces or do/end?

a = [1,2,3,4,5]


p a.map { |n|
    n*2
}  
#=> [2,4,6         


        

Answer 1

That's because the second line is interpreted as:

p(a.map) do ... end

instead of:

p(a.map do ... end)

The grammar is ambiguous in this case and do doesn't seem to bind as strongly as {.