Question

I remember somewhere seeing such a notation for formally defining a variable:

variable_name: type

And similarly:

function_name(....): return_type

But I don’t remember and I can’t find the formal definition of this syntax.

My question first is, is this really a formal syntax or did somebody just make it up? My second question, can you give me the name for it, or a reference?

I am asking because I was wondering how the function arguments are defined. Would it be like this?

function(arg1:type1, arg2:type2): type

If so, how are default values shown?

Answer 1

The syntax you describe is used in the ML family of programming languages. In Standard ML, which has a formal semantics, there are no default values, everything must be initialized when declared.