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(.module:
[lux #*
["." io]
[control
["M" monad (#+ Monad do)]
pipe
["&" writer]]
[data
["." product]
["." text ("text/." equivalence)]]]
lux/test)
(context: "Writer."
(let [(^open "&/.") (&.monad text.monoid)
(^open "&/.") (&.apply text.monoid)]
($_ seq
(test "Functor respects Writer."
(i/= +11 (product.right (&/map inc ["" +10]))))
(test "Apply respects Writer."
(and (i/= +20 (product.right (&/wrap +20)))
(i/= +30 (product.right (&/apply (&/wrap (i/+ +10)) (&/wrap +20))))))
(test "Monad respects Writer."
(i/= +30 (product.right (do (&.monad text.monoid)
[f (wrap i/+)
a (wrap +10)
b (wrap +20)]
(wrap (f a b))))))
(test "Can log any value."
(text/= "YOLO" (product.left (&.log "YOLO"))))
)))
(context: "Monad transformer"
(let [lift (&.lift text.monoid io.monad)
(^open "io/.") io.monad]
(test "Can add writer functionality to any monad."
(|> (io.run (do (&.WriterT text.monoid io.monad)
[a (lift (io/wrap +123))
b (wrap +456)]
(wrap (i/+ a b))))
(case> ["" +579] #1
_ #0)))
))
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