Monads/Writer monad: Difference between revisions
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</lang>
=={{header|Factor}}==
Factor comes with an implementation of Haskell-style monads in the <code>monads</code> vocabulary. Due to what may be a bug, the log reads backward. This can be rectified by redefining the <code>writer</code> method for <code>>>=</code> to say <code>prepend</code> instead of <code>append</code>. I will run this by the language maintainers and hopefully the redefinition can be removed in the future.
<lang factor>USING: kernel math math.functions monads prettyprint sequences ;
FROM: monads => do ;
M: writer >>=
[ run-writer ] curry
[ dip [ run-writer ] compose dip prepend <writer> ] curry ;</lang>
Now we can get on with it:
<lang factor>{
[ 5 "Started with five, " <writer> ]
[ sqrt "took square root, " <writer> ]
[ 1 + "added one, " <writer> ]
[ 2 / "divided by two." <writer> ]
} do .</lang>
{{out}}
<pre>
T{ writer
{ value 1.618033988749895 }
{ log
"Started with five, took square root, added one, divided by two."
}
}
</pre>
=={{header|Go}}==
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