do block vs. begin block in Julia

dotest.jl

dofun(f) = f()

macro gendo()
    ex = Expr(:block)
    for i in 1:10000
        push!(ex.args, :(dofun() do
            1+$i
        end))
    end
    ex
end

function rundo()
    @gendo
end

macro genbegin()
    ex = Expr(:block)
    for i in 1:10000
        push!(ex.args, :(begin
            1+$i
        end))
    end
    ex
end

function runbegin()
    @genbegin
end

@time @gendo
# 6.942990 seconds (208.73 k allocations: 13.143 MB, 0.13% gc time)
# 6.426416 seconds (208.47 k allocations: 13.125 MB, 0.13% gc time)

@time @genbegin
# 0.001050 seconds (9.49 k allocations: 148.438 KB)
# 0.001246 seconds (9.49 k allocations: 148.438 KB)

@time rundo()
# 76.339691 seconds (1.58 M allocations: 83.071 MB, 0.04% gc time)
# 0.001713 seconds (9.49 k allocations: 148.438 KB)

@time runbegin()
# 0.253740 seconds (1.38 M allocations: 67.851 MB, 8.61% gc time)
# 0.000001 seconds (5 allocations: 176 bytes)