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copied!<p>In my opinion most, if not all, compiler does not verify that a function exists at compilation. What it is required in general is a prototype declaration of the function: the type of the return value, the list and type of all arguments. This is done in C/C++ by including some_file.h in each module definition (not the .c or .cpp). </p> <p>In Erlang this type verification is done dynamically, while the program is running, so it is not necessary to include these definitions. It is even totally useless because Erlang allows to upgrade the application in run, so the function type may change, or the function may disappear, on purpose or by mistake, during application life time; it is why the Erlang designer have chosen to make this verification at run time and not at build time.</p> <p>The error you speak about generally occurs during the link phase of the code generation, when the "compiler" tries to gather all together some individual pieces of object code to build an executable file or a library, during this phase the linker solves all the external addresses (for shared variable, static call...). This phase does not exist in Erlang, a module is totally self contained; it does no share anything with the rest of the application, no variable nor function address.</p> <p>Of course, it is mandatory to use some tools and make some test before updating a running production program, but I consider that these verifications have exactly the same level of importance than the correctness of the algorithm itself.</p>

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