"\&" - is used while bullet proofing a program because it permits runtime error to exit my program so sudden. so the programmer could easily notice the error.

"eval" - is used when you have finished bullet proofing a program. well it just trap runtime errors that was not caught by the programmer.

<update>

No, the difference is that \& { } constructs a reference to a subroutine which is named after whatever it is the evaluation of the contents of { } returns. That is, \& {chr(65)} returns a reference to the subroutine A, be this sub defined or not. In your example, a subroutine is allocated in the symbol table named after the return value of exit or yes\n, depending on the input. Which is a weird form to shoehorn something into the symbol table.

</update>

<No, the difference is that \& { } constructs a code reference from a block (which isn't even a subroutine, just a code reference) which is a reference to a subroutine , while eval { } ... well, evals the { } block. So, \& { } is just bare metal, without the additional features eval { } provides.

One could say \& { } is to eval { } what do is to require, if that helps (it's not quite so).

I don't know the compile time implications of \& { }, but I suspect them to be the same as with eval { } - this all isn't about bullet proofing, but - again - I might be wrong.

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