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[DMS-68] Use direct recursion in folding functions #12

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[DMS-68] Use direct recursion in folding functions #12

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03e9ab5
Reuse iteration code and parametrize it with map walking function
s-and-witch Oct 11, 2024
11613a5
Use direct recursion in folding functions
s-and-witch Oct 9, 2024
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63 changes: 39 additions & 24 deletions src/PersistentOrderedMap.mo
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Original file line number Diff line number Diff line change
Expand Up @@ -324,30 +324,39 @@ module {
///
/// Note: Full map iteration creates `O(n)` temporary objects that will be collected as garbage.
public func iter<K, V>(rbMap : Map<K, V>, direction : Direction) : I.Iter<(K, V)> {
object {
var trees : IterRep<K, V> = ?(#tr(rbMap), null);
public func next() : ?(K, V) {
switch (direction, trees) {
case (_, null) { null };
case (_, ?(#tr(#leaf), ts)) {
let turnLeftFirst : MapTraverser<K, V>
= func (l, xy, r, ts) { ?(#tr(l), ?(#xy(xy), ?(#tr(r), ts))) };

let turnRightFirst : MapTraverser<K, V>
= func (l, xy, r, ts) { ?(#tr(r), ?(#xy(xy), ?(#tr(l), ts))) };

switch direction {
case (#fwd) IterMap(rbMap, turnLeftFirst);
case (#bwd) IterMap(rbMap, turnRightFirst)
}
};

type MapTraverser<K, V> = (Map<K, V>, (K, V), Map<K, V>, IterRep<K, V>) -> IterRep<K, V>;

class IterMap<K, V>(rbMap : Map<K, V>, mapTraverser : MapTraverser<K, V>) {
var trees : IterRep<K, V> = ?(#tr(rbMap), null);
public func next() : ?(K, V) {
switch (trees) {
case (null) { null };
case (?(#tr(#leaf), ts)) {
trees := ts;
next()
};
case (_, ?(#xy(xy), ts)) {
case (?(#xy(xy), ts)) {
trees := ts;
?xy
}; // TODO: Let's float-out case on direction
case (#fwd, ?(#tr(#node(_, l, xy, r)), ts)) {
trees := ?(#tr(l), ?(#xy(xy), ?(#tr(r), ts)));
next()
};
case (#bwd, ?(#tr(#node(_, l, xy, r)), ts)) {
trees := ?(#tr(r), ?(#xy(xy), ?(#tr(l), ts)));
case (?(#tr(#node(_, l, xy, r)), ts)) {
trees := mapTraverser(l, xy, r, ts);
next()
}
}
}
}
};

/// Returns an Iterator (`Iter`) over the key-value pairs in the map.
Expand Down Expand Up @@ -527,11 +536,14 @@ module {
combine : (Key, Value, Accum) -> Accum
) : Accum
{
var acc = base;
for(val in iter(rbMap, #fwd)){
acc := combine(val.0, val.1, acc);
};
acc
switch (rbMap) {
case (#leaf) { base };
case (#node(_, l, (k, v), r)) {
let left = foldLeft(l, base, combine);
let middle = combine(k, v, left);
foldLeft(r, middle, combine)
}
}
};

/// Collapses the elements in `rbMap` into a single value by starting with `base`
Expand Down Expand Up @@ -567,11 +579,14 @@ module {
combine : (Key, Value, Accum) -> Accum
) : Accum
{
var acc = base;
for(val in iter(rbMap, #bwd)){
acc := combine(val.0, val.1, acc);
};
acc
switch (rbMap) {
case (#leaf) { base };
case (#node(_, l, (k, v), r)) {
let right = foldRight(r, base, combine);
let middle = combine(k, v, right);
foldRight(l, middle, combine)
}
}
};


Expand Down