Pangea Pangea - 2 months ago 22
Scala Question

Circular Generators hanging indefinately

I have a set of names in a file. I need to implement a Generator that iterates through them continually. However, the code is hanging indefinitely at

if (iter.hasNext)
after the first pass.

Gen code

var asStream = getClass.getResourceAsStream("/firstnames/female/en_US_sample.txt")

var source: BufferedSource = Source.fromInputStream(asStream)
var iter: Iterator[String] = Iterator.continually(source.getLines()).flatten

val genLastName: Gen[String] = {
genCannedData
}

def genCannedData: Gen[String] = {
println("Generating names: " + iter)
Gen.delay {
if (iter.hasNext) {
println("In if")
Gen.const(iter.next)
}
else {
println("In else")
Gen.const(iter.next)
}
}
}


Sample Property test

property("FirstNames") = {
forAll(genLastName) {
a => {
println(a)
a == a
}
}
}


en_US_sample.txt file contents

Abbie
Abby
Abigail
Ada
Adah


EDIT- Temporary working code

The following code works if I recreate the iterator but I was wondering why
Iterator.continually
is hanging?

def genCannedData: Gen[String] = {
Gen.delay {
if (iter.hasNext) {
Gen.const(iter.next)
}
else {
asStream = getClass.getResourceAsStream("/firstnames/female/en_US_sample.txt")
source = Source.fromInputStream(asStream)
iter = source.getLines()
Gen.const(iter.next)
}
}
}

Answer

After first iteration, an iterator returned by source.getLines() returns false for hasNext, which means an empty iterator. Iterator.continually() continually evaluate source.getLines() expecting a next iterator, but it continues to return an empty iterator. Then it forms an infinite loop.