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Procedural macro backing monadify's do-notation.

This crate exports a single procedural macro, [mdo], which is re-exported by monadify under the non-default do-notation feature as monadify::mdo.

What it does

mdo! desugars an imperative monadic block — a sequence of let, pat <- expr;, guard(expr);, and bare expr; statements followed by a trailing final expression — into nested Marker::bind(..) calls over monadify's Bind / Applicative trait hierarchy.

The block names its Kind marker explicitly (marker inference is impossible because the GAT Of<Arg> is not injective):

use monadify::{mdo, OptionKind, Applicative};

let r: Option<i32> = mdo! { OptionKind;
    x <- Some(2);
    y <- Some(3);
    guard(x + y > 0);
    OptionKind::pure(x + y)      // raw monadic value, == Some(5)
};

A runnable version of this example lives on monadify::mdo (the gated re-export), where it can depend on monadify without a build cycle.

monadify-macros 0.1.1

What it does