Monads/Writer monad: Difference between revisions

=={{header|Julia}}==

<lang julia>struct Writer x::Real; msg::String; end

Base.show(io::IO, w::Writer) = print(io, w.msg, ": ", w.x)

unit(x, logmsg) = Writer(x, logmsg)

bind(f, fmsg, w) = unit(f(w.x), fmsg)

f1(x) = 7x

f2(x) = x + 8

a = unit(3, "after intialization")

b = bind(f1, " after times 7 ", a)

c = bind(f2, " after plus 8", b)

println("$a => $b => $c")

</lang>{{out}}

<pre>

after intialization: 3 => after times 7 : 21 => after plus 8: 29

</pre>