Declaration parameters are followed by a type (the reverse of some programming
languages), then a return type.
The last expression in a function body (or any block) becomes the return
value. Simply omit the ; at the end of the expression. The return keyword
can be used for early return, but the “bare value” form is idiomatic at the
end of a function (refactor gcd to use a return).
Some functions have no return value, and return the ‘unit type’, (). The
compiler will infer this if the return type is omitted.
Overloading is not supported – each function has a single implementation.
Always takes a fixed number of parameters. Default arguments are not
supported. Macros can be used to support variadic functions.
Always takes a single set of parameter types. These types can be generic,
which will be covered later.