Monads/Writer monad: Difference between revisions
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# Apply a composition of the Writer versions of root, addOne, and half to the integer 5, deriving both a value for the Golden Ratio φ, and a concatenated log of the function applications (starting with the initial value, and followed by the application of root, etc.)
=={{header|J}}==
Based on javascript implementation:
<lang J>root=: %:
incr=: >:
half=: -:
tostr=: ,@":
loggingVersion=: conjunction define
n;~u
)
Lroot=: root loggingVersion 'obtained square root'
Lincr=: incr loggingVersion 'added 1'
Lhalf=: half loggingVersion 'divided by 2'
loggingUnit=: verb define
y;'Initial value: ',tostr y
)
loggingBind=: adverb define
r=. u 0{::y
v=. 0{:: r
v;(1{::y),LF,(1{::r),' -> ',tostr v
)
loggingCompose=: dyad define
;(dyad def '<x`:6 loggingBind;y')/x,<loggingUnit y
)</lang>
Task example:
<lang J> 0{::Lhalf`Lincr`Lroot loggingCompose 5
1.61803
1{::Lhalf`Lincr`Lroot loggingCompose 5
Initial value: 5
obtained square root -> 2.23607
added 1 -> 3.23607
divided by 2 -> 1.61803</lang>
=={{header|JavaScript}}==
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