Monads/Writer monad: Difference between revisions
added Raku programming solution
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add one: 3.2360679774998
half: 1.6180339887499
</pre>
=={{header|Raku}}==
Basic semantic borrowed from the Monads/List monad entry
{{trans|Go}}
<lang raku># 20200508 Raku programming solution
class Writer { has Numeric $.value ; has Str $.log }
sub Bind (Writer \v, &code) {
my \n = v.value.&code;
Writer.new: value => n.value, log => v.log ~ n.log
};
sub Unit(\v, \s) { Writer.new: value=>v, log=>sprintf "%-17s: %.12f\n",s,v}
sub root(\v) { Unit v.sqrt, "Took square root" }
sub addOne(\v) { Unit v+1, "Added one" }
sub half(\v) { Unit v/2, "Divided by two" }
say Unit(5, "Initial value").&Bind(&root).&Bind(&addOne).&Bind(&half).log;</lang>
{{out}}
<pre>Initial value : 5.000000000000
Took square root : 2.236067977500
Added one : 3.236067977500
Divided by two : 1.618033988750
</pre>
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