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copied!<p>The article you link is based on sigfpe's article, which uses a flipped definition of bind:</p> <blockquote> <p>The first thing is that I've flipped the definition of <code>bind</code> and written it as the word 'bind' whereas it's normally written as the operator <code>>>=</code>. So <code>bind f x</code> is normally written as <code>x >>= f</code>.</p> </blockquote> <p>So, the Haskell <code>bind</code> takes a value enclosed in a monad, and returns a function, which takes a function and then calls it with the extracted value. I might be using non-precise terminology, so maybe better with code.</p> <p>You have:</p> <pre><code>sine x = (sin x, "sine was called.") cube x = (x * x * x, "cube was called.") </code></pre> <p>Now, translating your JS bind (Haskell does automatic currying, so calling <code>bind f</code> returns a function that takes a tuple, and then pattern matching takes care of unpacking it into <code>x</code> and <code>s</code>, I hope that's understandable):</p> <pre><code>bind f (x, s) = (y, s ++ t) where (y, t) = f x </code></pre> <p>You can see it working:</p> <pre><code>*Main> :t sine sine :: Floating t => t -> (t, [Char]) *Main> :t bind sine bind sine :: Floating t1 => (t1, [Char]) -> (t1, [Char]) *Main> (bind sine . bind cube) (3, "") (0.956375928404503,"cube was called.sine was called.") </code></pre> <p>Now, let's reverse arguments of <code>bind</code>:</p> <pre><code>bind' (x, s) f = (y, s ++ t) where (y, t) = f x </code></pre> <p>You can clearly see it's still doing the same thing, but with a bit different syntax:</p> <pre><code>*Main> bind' (bind' (3, "") cube) sine (0.956375928404503,"cube was called.sine was called.") </code></pre> <p>Now, Haskell has a syntax trick that allows you to use any function as an infix operator. So you can write:</p> <pre><code>*Main> (3, "") `bind'` cube `bind'` sine (0.956375928404503,"cube was called.sine was called.") </code></pre> <p>Now rename <code>bind'</code> to <code>>>=</code> (<code>(3, "") >>= cube >>= sine</code>) and you've got what you were looking for. As you can see, with this definition, you can effectively get rid of the separate composition operator.</p> <p>Translating the new thing back into JavaScript would yield something like this (notice that again, I only reverse the argument order):</p> <pre><code>var bind = function(tuple) { return function(f) { var x = tuple[0], s = tuple[1], fx = f(x), y = fx[0], t = fx[1]; return [y, s + t]; }; }; // ugly, but it's JS, after all var f = function(x) { return bind(bind(x)(cube))(sine); } f([3, ""]); // [0.956375928404503, "cube was called.sine was called."] </code></pre> <p>Hope this helps, and not introduces more confusion — the point is that those two bind definitions are equivalent, only differing in call syntax.</p>

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