org.petitparser.utils.Functions Maven / Gradle / Ivy
package org.petitparser.utils;
import org.petitparser.parser.Parser;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
/**
* Constructor and utility methods for functions.
*/
public class Functions {
private Functions() { }
/**
* Returns a function that returns the first value of a list.
*/
public static Function, T> firstOfList() {
return list -> list.get(0);
}
/**
* Returns a function that returns the last value of a list.
*/
public static Function, T> lastOfList() {
return list -> list.get(list.size() - 1);
}
/**
* Returns a function that returns the value at the given index. Negative
* indexes are counted from the end of the list.
*/
public static Function, T> nthOfList(int index) {
return list -> list.get(index < 0 ? list.size() + index : index);
}
/**
* Returns a function that returns the permutation of a given list. Negative
* indexes are counted from the end of the list.
*/
public static Function, List> permutationOfList(
int... indexes) {
return list -> {
List result = new ArrayList<>(indexes.length);
for (int index : indexes) {
result.add(list.get(index < 0 ? list.size() + index : index));
}
return result;
};
}
/**
* Returns a function that skips the separators of a given list, see {@link
* Parser#separatedBy(Parser)}.
*/
public static Function, List> withoutSeparators() {
return list -> {
List result = new ArrayList<>();
for (int i = 0; i < list.size(); i += 2) {
result.add(list.get(i));
}
return result;
};
}
/**
* Returns a function that returns a constant value.
*/
public static Function constant(T output) {
return input -> output;
}
}