But nobody uses call/cc in Ruby in practice. The issue with Ruby performance is immature VM's/compilers.
There are tons of performance killers in Ruby, but most of them can be "worked around" by making assumptions about the common case and "just" spend some cycles verifying when the assumptions are violated.
E.g. 99.99% of the time, noone are stupid enough to redefine integer addition (because, besides the fact there aren't many good reasons to, all kinds of hell breaks loose if you do, for obvious reasons), so you can usually check the type tag on integers and inline the addition.
The problem is that edge case. But the edge case can be detected when someone tries to redefine '+' and you'd still save massive amounts of time if you were to set a flag at that point and still inline the additions, just with a test and branch to a slow path if people does something stupid (or in the case of JIT's, "just" re-jit everything at that point - yes, then overriding '+' will be slow, but common code will be much faster).
There are tons of performance killers in Ruby, but most of them can be "worked around" by making assumptions about the common case and "just" spend some cycles verifying when the assumptions are violated.
E.g. 99.99% of the time, noone are stupid enough to redefine integer addition (because, besides the fact there aren't many good reasons to, all kinds of hell breaks loose if you do, for obvious reasons), so you can usually check the type tag on integers and inline the addition.
The problem is that edge case. But the edge case can be detected when someone tries to redefine '+' and you'd still save massive amounts of time if you were to set a flag at that point and still inline the additions, just with a test and branch to a slow path if people does something stupid (or in the case of JIT's, "just" re-jit everything at that point - yes, then overriding '+' will be slow, but common code will be much faster).