README.md

MoreExpressions.Fody

Fody weaver that adds new expressions to .NET through method calls.

This is mainly developed with F# in mind, and currently doesn't really work. The tests pass though, which probably means something.

return expression

Transforms any call to MoreExpressions.Return to a return expression.

let ``return inside expression``() =
    let a =
        if return' 0 then
            1
        else
            2

    a

let ``return zero instead of one``() =
    return' 0

    1

Both of the above functions return 0. In C#, you could write the following:

int ReturnInsideExpression()
{
    int a = 2;

    if (MoreExpressions.Return(0))
        a = 1;

    return a;
}

int ReturnZeroInsteadOfOne()
{
    MoreExpressions.Return(0);

    return 1;
}

Using MoreExpressions.Return, more powerful functions can be implemented; for instance, the Rust try! macro is trivial to add to F#:

let inline try' option =
    match option with
    | Some value -> value
    | None -> return' None

This can be used this way:

let ``only even numbers``(i : int) =
    if i % 2 = 0 then
        Some i
    else
        None

let x =
    let a = try' (``only even numbers`` 1)
    let b = try' (``only even numbers`` 2)

    Some (a + b)

let y =
    let a = try' (``only even numbers`` 2)
    let b = try' (``only even numbers`` 4)

    Some (a + b)

Obviously, x will be None (because 1 is not even) and y will be Some 6 (because both 2 and 4 are even).

label, jump expressions

The mklabel function returns a pair of functions that can be used to implement jumps in your F# code.

let label, jump = mklabel

for i = 0 to n - 1 do
    let isOver = complicatedComputation i n

    if isOver then
        jump true

let endedEarly = label false

The first function, label, takes a default value and either returns this value if the label expression is reached naturally, or the expression passed to jump otherwise.

In the example above, if complicatedComputation i n returns true, then jump true will be called which will immediately jump to the endedEarly assignment; here, label false will return true.

If instead complicatedComputation i n never returned true, then label false would return its default value; that is, false.

Do watch out, though: anything that happens between jump and label will not be invoked in case of a jump, which is extremely unsafe (it will break your stack and break all variables that should have been in the meantime). Therefore this structure should only be used in very specific circumstances.

Gotchas

Since IL code is modified, so things that rely on local variables like F# quotations may not work in functions that use one of the above expressions.