defmodule MyLib do
require MyMath
def go(), do: MyMath.calc(1, 2)
end
Here’s the MyMath module:
my_math.exs:
defmodule MyMath do
def calc(x, y), do: x+y
end
Both files are in the same directory. Here is what I get:
~/elixir_programs$ iex my_lib.exs
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
** (CompileError) my_lib.exs:2: module MyMath is not loaded and could not be found
require does not look for files at all, the module has to be already loaded in order for it to work in the way you are trying. If you add to the top of your file Code.require_file("my_math.exs"), you should see it start working. If you do $ mix new my_project and put these files in lib (as .ex files not .exs) you won’t need to do anything and the compiler will find the right file automatically; this is the typical way to do things. After that, run $ iex -S mix and your code will be available for execution (type into the prompt MyLib.go()).
As for the code you’ve written, you don’t need a require statement at all. Requires are for loading macros before they’re used, which your function is not (its just a plain function). You can remove the require MyMath and everything will still work fine.
You can read more about alias, require, import and use here: https://elixir-lang.org/getting-started/alias-require-and-import.html
Related to this: A file containing a module with a name like Foo.Bar.Baz is placed in foo/bar/ and named baz.exby convention, but there is nothing stopping you from doing it differently (except the very strong argument of confused coworkers).
Sometimes there are reasons for not following this convention though, for instance when having (for programmatic reasons) to define multiple modules in the same file.
You should be using *.ex files not *.exs files. The latter are only compiled in memory and beam files are not written to disk, which is why MyMath cannot be found. For a minimal fix, just rename my_math.exs to my_math.ex
It’s not clear from what you’ve shown whether you’re in a mix project and whether you’ve compiled my_math.ex to generate a beam file. If you’re not using mix, then you need to compile by hand.
$ elixirc my_math.ex
will generate a file in the current directory called Elixir.MyMath.beam. Now that you have a beam file, it can be called in your exs script.
If you’re not using mix, then you need to compile by hand.
$ elixirc my_math.ex
Okay, that worked…but it also worked without the require statement, so I guess I don’t understand what require does yet:
As for the code you’ve written, you don’t need a require statement at all. Requires are for loading macros before they’re used, which your function is not (its just a plain function). You can remove the require MyMath and everything will still work fine.
The problem is that the book I’m reading hasn’t covered macros yet, but in the code examples there are lines with require, use, and import statements.
require in Elixir is not like require in your prior language. That quote you included from @mgwidmann explains it well. require is about macros, and you’re not using macros.
Without a doubt you are causing yourself more headache than its worth. Create a new mix project and put the files in lib and call it a day. Mix makes this easy for this very reason.
require does not look for files at all, the module has to be already loaded
Why does elixir make you require a module before you can call the macros defined in the module? I don’t have to import a module before I call the functions defined in the module.
Calling function happens at runtime, where modules are already compiled. For macros modules are required to be compiled in a certain order, a.k.a. the module with the macros must be compiled before the module using those macros. This dependency in compilation order is set up by using require or import.
The order of compilation doesn’t matter with import because it is resolved at runtime. But the order of compilation matters with macros specifically because they happen at compile time.
Because macros can change semantics of the core language constructs, you have to explicitly opt-in into using them. This was a very early design decision.