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Nuove funzioni ricorsive

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This commit is contained in:
Fabio Scotto di Santolo
2020-01-28 14:06:07 +01:00
parent d61c649e16
commit 5ea972150b
1 changed files with 29 additions and 5 deletions
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34
functional-programming-java/src/main/java/org/gym/fp/fpjava/type/CollectionUtilities.java
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@@ -5,6 +5,9 @@ import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import static org.gym.fp.fpjava.type.TailCall.ret;
import static org.gym.fp.fpjava.type.TailCall.suspend;
public final class CollectionUtilities {
public static <T> List<T> list() {
@@ -54,11 +57,21 @@ public final class CollectionUtilities {
// ES. 3.6
public static <T, U> U foldLeft(List<T> list, U identity, Function<U, Function<T, U>> f) {
U result = identity;
for (T e : list) {
result = f.apply(result).apply(e);
}
return result;
/*
U result = identity;
for (T e : list) {
result = f.apply(result).apply(e);
}
return result;
*/
return _foldLeft(list, identity, f).eval();
}
// ES. 4.3
private static <T, U> TailCall<U> _foldLeft(List<T> list, U identity, Function<U, Function<T, U>> f) {
return list.isEmpty()
? ret(identity)
: suspend(() -> _foldLeft(tail(list), f.apply(identity).apply(head(list)), f));
}
// ES. 3.7
@@ -120,6 +133,17 @@ public final class CollectionUtilities {
return unfold(start, x -> x + 1, x -> x < end);
}
// ES. 4.4
public static List<Integer> rangeRec(int start, int end) {
return _range(list(), start, end).eval();
}
private static TailCall<List<Integer>> _range(List<Integer> acc, Integer start, Integer end) {
return end <= start
? ret(acc)
: suspend(() -> _range(append(acc, start), start + 1, end));
}
// ES. 3.12
public static <T> List<T> unfold(T seed, Function<T, T> f, Function<T, Boolean> predicate) {
List<T> result = list();