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May 24, 2017 19:10
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Monad Laws Example on scala List Monad
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/* | |
Monads laws examples with List monads | |
Summary from article: https://devth.com/2015/monad-laws-in-scala | |
*/ | |
val f: (Int => List[Int]) = x => List(x - 1, x, x + 1) | |
val g: (Int => List[Int]) = x => List(x, -x) | |
val unitX = List(2) //list monad | |
/* | |
left identity law: | |
unit(x).flatMap(f) == f(x) | |
*/ | |
val lhs=unitX.flatMap(f) | |
val rhs=f(1) | |
println(lhs) | |
println (rhs) | |
println(lhs==rhs) | |
/* | |
right-identity law: | |
unit(x).flatMap(unit) ==unit(x) | |
*/ | |
val lhs1 = unitX.flatMap(x=>List(x)) | |
val rhs1=unitX | |
println(lhs1) | |
println(rhs1) | |
println(lhs1==rhs1) | |
/* | |
associativity law: | |
unit(x).flatMap(f).flatMap(g) == unit(x).flatMap(x ⇒ f(x).flatMap(g)) | |
*/ | |
val lhs2=unitX.flatMap(f).flatMap(g) | |
val rhs2=unitX.flatMap(x=>f(x).flatMap(g)) | |
println(lhs2) | |
println(rhs2) | |
println(lhs2==rhs2) |
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