functional programming - inexplicable for-comprehension result in Scala -


this question has answer here:

i understand for-expression translated map , flatmap. found can not explain , need helps. here 2 toy examples:

for {     none <- list(option(1),none) } yield 0  //res0: list[int] = list(0, 0)

q1: why some(1) map 0 ? expecting list(0),

update1:
comment of @marios , ths 1 more bizarre.
for(none <- list(some(1), none) ) yield none returns list(some(1), none).

update2:
says variable, in ide, links none object.

i use intellij auto-translate above for-expression map-expression:

list(option(1), none).map { case none => 0 }    //scala.matcherror: some(1)

q2: error map-expression expected, while for-expression in first question doesn't give me error. why different computation ?

this appears bug in scala compiler. scala language specification states: "in first step, every generator p <- e, p not irrefutable type of e replaced p <- e.withfilter { case p => true; case _ => false }", , "a comprehension (p <- e) yield e′ translated e.map { case p => e′ }."

this means example, for { none <- list(option(1), none) } yield 0, should translated 

list(option(1),none).withfilter { case none => true; case _ => false }.map{case none => 0}

which evaluates list(0), expected.


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