Substitute while loop with functional code - scala

Question

I am refactoring some scala code and I am having problems with a while loop. The old code was:
for (s <- sentences){
// ...
while (/*Some condition*/){
// ...
function(trees, ...)
}
}
I've have translated that code into this one, using foldLeft to transverse sentences:
sentences./:(initialSeed){
(seed, s) =>
// ...
// Here I've replaced the while with other foldleft
trees./:(seed){
(v, n) =>
// ....
val updatedVariable = function(...., v)
}
}
Now, It may be the case that I need to stop transversing trees (The inner foldLeft before it is transverse entirely, for that I've found this question:
Abort early in a fold
But I also have the following problem:
As I transverse trees, I need to accumulate values to the variable v, function takes v and returns an updated v, called here updatedVariable. The problem is that I have the feeling that this is not a proper way of coding this functionality.
Could you recommended me a functional/immutable way of doing this?
NOTE: I've simplified the code to show the actual problem, the complete code is this:
val trainVocabulart = sentences./:(Vocabulary()){
(vocab, s) =>
var trees = s.tree
var i = 0
var noConstruction = false
trees./:(vocab){
(v, n) =>
if (i == trees.size - 1) {
if (noConstruction) return v
noConstruction = true
i = 0
} else {
// Build vocabulary
val updatedVocab = buildVocabulary(trees, v, i, Config.LeftCtx, Config.RightCtx)
val y = estimateTrainAction(trees, i)
val (newI, newTrees) = takeAction(trees, i, y)
i = newI
trees = newTrees
// Execute the action and modify the trees
if (y != Shift)
noConstruction = false
Vocabulary(v.positionVocab ++ updatedVocab.positionVocab,
v.positionTag ++ updatedVocab.positionTag,
v.chLVocab ++ updatedVocab.chLVocab,
v.chLTag ++ updatedVocab.chLTag,
v.chRVocab ++ updatedVocab.chRVocab,
v.chRTag ++ updatedVocab.chRTag)
}
v
}
}
And the old one:
for (s <- sentences) {
var trees = s.tree
var i = 0
var noConstruction = false
var exit = false
while (trees.nonEmpty && !exit) {
if (i == trees.size - 1) {
if (noConstruction) exit = true
noConstruction = true
i = 0
} else {
// Build vocabulary
buildVocabulary(trees, i, LeftCtx, RightCtx)
val y = estimateTrainAction(trees, i)
val (newI, newTrees) = takeAction(trees, i, y)
i = newI
trees = newTrees
// Execute the action and modify the trees
if (y != Shift)
noConstruction = false
}
}
}

Answer 1

1st - You don't make this easy. Neither your simplified or complete examples are complete enough to compile.
2nd - You include a link to some reasonable solutions to the break-out-early problem. Is there a reason why none of them look workable for your situation?
3rd - Does that complete example actually work? You're folding over a var ...
trees./:(vocab){
... and inside that operation you modify/update that var ...
trees = newTrees
According to my tests that's a meaningless statement. The original iteration is unchanged by updating the collection.
4th - I'm not convinced that fold is what you want here. fold iterates over a collection and reduces it to a single value, but your aim here doesn't appear to be finding that single value. The result of your /: is thrown away. There is no val result = trees./:(vocab){...
One solution you might look at is: trees.forall{ ... At the end of each iteration you just return true if the next iteration should proceed.