Monads/Writer monad: Difference between revisions
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Thundergnat (talk | contribs) (Promote to task, lots of examples, little controversy) |
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Added one : 3.236067977500
Divided by two : 1.618033988750
</pre>
=={{header|Wren}}==
{{trans|Go}}
{{libheader|Wren-fmt}}
<lang ecmascript>import "/fmt" for Fmt
class Mwriter {
construct new(value, log) {
_value = value
_log = log
}
value { _value }
log {_log}
log=(value) { _log = value }
bind(f) {
var n = f.call(_value)
n.log = _log + n.log
return n
}
static unit(v, s) { Mwriter.new(v, " %(Fmt.s(-17, s)): %(v)\n") }
}
var root = Fn.new { |v| Mwriter.unit(v.sqrt, "Took square root") }
var addOne = Fn.new { |v| Mwriter.unit(v + 1, "Added one") }
var half = Fn.new { |v| Mwriter.unit( v / 2, "Divided by two") }
var mw1 = Mwriter.unit(5, "Initial value")
var mw2 = mw1.bind(root).bind(addOne).bind(half)
System.print("The Golden Ratio is %(mw2.value)")
System.print("\nThis was derived as follows:-")
System.print(mw2.log)</lang>
{{out}}
<pre>
The Golden Ratio is 1.6180339887499
This was derived as follows:-
Initial value : 5
Took square root : 2.2360679774998
Added one : 3.2360679774998
Divided by two : 1.6180339887499
</pre>
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