InternalFunctors.java

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 * Copyright (C) Codehaus.org                                                *
 * ------------------------------------------------------------------------- *
 * Licensed under the Apache License, Version 2.0 (the "License");           *
 * you may not use this file except in compliance with the License.          *
 * You may obtain a copy of the License at                                   *
 *                                                                           *
 * http://www.apache.org/licenses/LICENSE-2.0                                *
 *                                                                           *
 * Unless required by applicable law or agreed to in writing, software       *
 * distributed under the License is distributed on an "AS IS" BASIS,         *
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  *
 * See the License for the specific language governing permissions and       *
 * limitations under the License.                                            *
 *****************************************************************************/
package net.ion.rosetta;

import net.ion.rosetta.functors.Map;
import net.ion.rosetta.functors.Map2;
import net.ion.rosetta.functors.Map3;
import net.ion.rosetta.functors.Map4;
import net.ion.rosetta.functors.Map5;

/**
 * Functors used only internally by this package.
 * 
 * @author Ben Yu
 */
final class InternalFunctors {

	static <T> TokenMap<T> isTokenType(final Class<T> targetType, final String name) {
		return new TokenMap<T>() {
			public T map(Token token) {
				if (targetType.isInstance(token.value())) {
					return targetType.cast(token.value());
				}
				return null;
			}

			@Override
			public String toString() {
				return name;
			}
		};
	}

	static TokenMap<Token> tokenWithSameValue(final Object value) {
		return new TokenMap<Token>() {
			public Token map(Token token) {
				return (value == token.value()) ? token : null;
			}

			@Override
			public String toString() {
				return String.valueOf(value);
			}
		};
	}

	@SuppressWarnings("unchecked")
	private static final Map2 FIRST_OF_TWO = new Map2() {
		public Object map(Object first, Object b) {
			return first;
		}

		@Override
		public String toString() {
			return "followedBy";
		}
	};

	@SuppressWarnings("unchecked")
	private static final Map2 LAST_OF_TWO = new Map2() {
		public Object map(Object a, Object last) {
			return last;
		}

		@Override
		public String toString() {
			return "sequence";
		}
	};

	@SuppressWarnings("unchecked")
	private static final Map3 LAST_OF_THREE = new Map3() {
		public Object map(Object a, Object b, Object last) {
			return last;
		}

		@Override
		public String toString() {
			return "sequence";
		}
	};

	@SuppressWarnings("unchecked")
	private static final Map4 LAST_OF_FOUR = new Map4() {
		public Object map(Object a, Object b, Object c, Object last) {
			return last;
		}

		@Override
		public String toString() {
			return "sequence";
		}
	};

	@SuppressWarnings("unchecked")
	private static final Map5 LAST_OF_FIVE = new Map5() {
		public Object map(Object a, Object b, Object c, Object d, Object last) {
			return last;
		}

		@Override
		public String toString() {
			return "sequence";
		}
	};

	@SuppressWarnings("unchecked")
	static <T, B> Map2<T, B, T> firstOfTwo() {
		return FIRST_OF_TWO;
	}

	@SuppressWarnings("unchecked")
	static <A, T> Map2<A, T, T> lastOfTwo() {
		return LAST_OF_TWO;
	}

	@SuppressWarnings("unchecked")
	static <A, B, T> Map3<A, B, T, T> lastOfThree() {
		return LAST_OF_THREE;
	}

	@SuppressWarnings("unchecked")
	static <A, B, C, T> Map4<A, B, C, T, T> lastOfFour() {
		return LAST_OF_FOUR;
	}

	@SuppressWarnings("unchecked")
	static <A, B, C, D, T> Map5<A, B, C, D, T, T> lastOfFive() {
		return LAST_OF_FIVE;
	}

	/**
	 * Returns a {@link Map} that delegates to {@code map} and falls back to {@code defaultMap} for null return values.
	 */
	public static <F, T> Map<F, T> fallback(final Map<F, T> map, final Map<? super F, ? extends T> defaultMap) {
		return new Map<F, T>() {
			public T map(F v) {
				T result = map.map(v);
				return (result == null) ? defaultMap.map(v) : result;
			}

			@Override
			public String toString() {
				return "fallback";
			}
		};
	}
}