I am trying to implement a library with extended parsing capabilities. I decided that I will use fsyacc because I knew it from the university. Unfortunately I encountered following problem.
I defined a class for the head of my grammar (Head) and place its implementation in a single file. Then I defined parser as:
...
%start head
%type <Head> head
...
Fsyacc generates seeparated module (Parser). In order to succeed it has to be compiled in following order: Head.fs Parser.fs
In order to make this library similar to what you can find in .NET I would like to add a static Parse method to Head. Unfortunately I would need to make use of methods from Parser module.
I know that such type dependencies can be solved with ‘and‘ operator but it is only applicable to types defined in one file.
Is there any other way to create types that depend on each other even when they are in separate files? I was looking for declaration/implementation separation mechanism like the one in C/C++ but I couldn’t find anything.
Short answer: no. There’s no way to do mutually recursive entities across multiple files in F# 2.0. (This is something we plan to address in the next version of the language.)
You can work around this in a variety of ways, typically using a point of indirection and mutation. For example, your Head type could have a static ‘InitializeParser’ method that pokes a function value into a mutable global variable, and then the static Parse method defined in Head could call via that mutable global, and after the parser is actually defined, it can go and call InitializeParser to poke the value in. (If that doesn’t make sense, I can spell it out in more detail.)