在解释和编译模式下都包含OCaml模块

Question

Say I have some OCaml code where I need to use the Str module. If I run the code with the interpreter, then I have to put #load Str.cma to be able to use the Str module. But if I want to native-compile the code, then the load directive causes an error. How can I import the module in a way that will work in both cases?

I'm looking for either
(a) a way to include the module that works in both modes; or
(b) a way to load the module for the interpreter that will be ignored by the compiler, leaving me to specify it on the command line.

Answer 1

You can use OCaml in a scripting way (using the ocaml binary, called toplevel), like you are describing. Scripts have the advantage that the code is readily accessible and changeable. But some problems arise:

• your script is bytecode compiled at each call, which is quite fast but far from optimal
• the directives for loading the packages you need are specific to the toplevel and not compatible with the compilers
• if you need one of the many packages from the ocaml package manager opam you must install opam globally which currently is linux admin work and not officially recommended

So there is no compatible syntax for ocaml toplevel and compiler invocation. Command line arguments for the toplevel would require another wrapper script.

My recommendation:

• use the toplevel for interactive development, exploration of features, and tests
• use the opam installer for your packages and the compiler, this will give you updatable tools
• compile your scripts to bytecode or native code depending on your requirements, compiled code is portable within the platform and fast

Compiling is quite simple for ocaml programs once you know how to specify the components.

As a side note: there is an opam package called ocamlscript that gives you a specific syntax for your packages and dependencies in a sort of script header, but compiles your script transparently to disk. Maybe this is what you want - but global opam install required.

Answer 2

I wouldn't put #load into the source file, it's not OCaml code. It's an instruction to the toplevel (as you know of course).

One possibility is to add the #load commands you need to your ~/.ocamlinit file. It doesn't hurt to load a few extra modules, so you can modify your ~/.ocamlinit only occasionally as you work on different things.

Answer 3

如果您希望能够执行ocaml my_code.ml并且my_code.ml使用Str模块，则只需执行ocaml str.cma my_code.ml 。