either monad

This is the C++ template metaprogramming equivalent of Haskell's Either monad. The purpose of this monad is to provide basic error handling for pure code. The either monad is similar to the exception monad, but it is more difficult to use because of treating every non-exception value as a result instead of introducing a new type, left for it. Compile-time exception handling is built on top of the exception monad.

Monadic values consist of left<T> and right<T>, where T is a nullary metafunction. Both left and right evaluate its argument. left represents error, right represents normal result.

General information

• header: <mpllibs/metamonad/either.hpp>
• tag of monad: either_tag
• return's logic: pass the argument to right
• bind's logic: when the first argument is left, bind returns it as it is. When it is right, bind passes the wrapped value to the continuation, the last argument of bind.
• fail's logic: wrap its argument with left

Copyright Abel Sinkovics (abel at elte dot hu) 2011. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt

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