hydra.lib.lists.Head Maven / Gradle / Ivy

Go to download
package hydra.lib.lists;

import hydra.Flows;
import hydra.compute.Flow;
import hydra.core.Name;
import hydra.core.Term;
import hydra.core.Type;
import hydra.dsl.Expect;
import hydra.graph.Graph;
import hydra.tools.PrimitiveFunction;
import java.util.List;
import java.util.function.Function;

import static hydra.Flows.map;
import static hydra.dsl.Types.function;
import static hydra.dsl.Types.lambda;
import static hydra.dsl.Types.list;


public class Head extends PrimitiveFunction {
    public Name name() {
        return new Name("hydra/lib/lists.head");
    }

    @Override
    public Type type() {
        return lambda("a", function(list("a"), "a"));
    }

    @Override
    protected Function>, Flow, Term>> implementation() {
        return args -> map(Expect.list(Flows::pure, args.get(0)), Head::apply);
    }

    /**
     * Apply the function to it single argument.
     */
    public static  X apply(List list) {
        if (list.isEmpty()) {
            throw new IllegalArgumentException("Cannot get head of empty list");
        } else {
            return list.get(0);
        }
    }
}