问题
Another question again :P I'm not too sure whether I should post it here or on the OCaml mailing list, but I try SO first.
I like assert statements. However, I find the error messages close to useless without an additional message (assertion violation at line XXX --- well great, but what actually went wrong?).
I think the good example of an assertion is a pythonic assert x > 0, "X must be greater than zero for the algorithm X to work" and a bad example is C-like assert(x>0).
I was quite disappointed to learn that there is no way to attach an error message to an assertion in OCaml =( My options are:
- Write a custom function, say
vassert=> but I won't get the magic line numbers which are only possible with theassertkeyword - Use
failwith, but it is considerably more verbose, and I think suffers from the same problem as a custom function. - Use functions from
OUnit, but I don't want to introduce unneeded dependency.
Does anyone else have the same problem? What do people use?
回答1:
A little bit tedious but works fine:
assert (if not cond then print_endline "your message"; cond)
回答2:
For me, the simpler way to dot that is to compile with the -g option and then add OCAMLRUNPARAM=b to the environment. This way you can write your own vassert, and you will get the whole stack trace that produced the call.
Of course, this is a result of my personal workflow were I consider assert as a debugging only tool that should never get seen by the final user.
来源：https://stackoverflow.com/questions/22561566/ocaml-assert-with-the-message