1 files changed, 106 insertions, 0 deletions
diff --git a/JPratt/src/main/java/com/ashardalon/pratt/tokens/TokenStream.java b/JPratt/src/main/java/com/ashardalon/pratt/tokens/TokenStream.java
new file mode 100644
index 0000000..3f2681b
--- /dev/null
+++ b/JPratt/src/main/java/com/ashardalon/pratt/tokens/TokenStream.java
@@ -0,0 +1,106 @@
+package com.ashardalon.pratt.tokens;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+import bjc.utils.funcutils.StringUtils;
+
+/**
+ * A stream of tokens.
+ *
+ * @author EVE
+ *
+ * @param <K>
+ *        The key type of the token.
+ *
+ * @param <V>
+ *        The value type of the token.
+ */
+public abstract class TokenStream<K, V> implements Iterator<Token<K, V>> {
+	/**
+	 * Get the current token.
+	 *
+	 * @return The current token.
+	 */
+	public abstract Token<K, V> current();
+
+	@Override
+	public abstract Token<K, V> next();
+
+	@Override
+	public abstract boolean hasNext();
+
+	/**
+	 * Place a mark in the current stream, which can be either returned to or abandoned later on.
+	 */
+	public abstract void mark();
+	
+	/**
+	 * Reset the stream to the state it was in when the last mark was taken.
+	 */
+	public abstract void rollback();
+	
+	/**
+	 * Check if the stream has at least one mark.
+	 * 
+	 * @return Whether or not at least one mark exists.
+	 */
+	public abstract boolean hasMark();
+	
+	/**
+	 * Remove the last mark placed into the stream. This prevents returning to it later on.
+	 */
+	public abstract void commit();
+	
+	/**
+	 * Utility method for checking that the next token is one of a specific
+	 * set of types, and then consuming it.
+	 *
+	 * @param expectedKeys
+	 *        The expected values
+	 *
+	 * @throws ExpectionNotMet
+	 *         If the token is not one of the expected types.
+	 */
+	public void expect(final Set<K> expectedKeys) throws ExpectionNotMet {
+		final K curKey = current().getKey();
+
+		if(!expectedKeys.contains(curKey)) {
+			final String expectedList = StringUtils.toEnglishList(expectedKeys.toArray(), false);
+
+			throw new ExpectionNotMet("One of '" + expectedList + "' was expected, not " + curKey);
+		}
+
+		next();
+	}
+
+	/**
+	 * Utility method for checking that the next token is one of a specific
+	 * set of types, and then consuming it.
+	 *
+	 * @param expectedKeys
+	 *        The expected values
+	 *
+	 * @throws ExpectionNotMet
+	 *         If the token is not one of the expected types.
+	 */
+	@SafeVarargs
+	public final void expect(final K... expectedKeys) throws ExpectionNotMet {
+		HashSet<K> keys = new HashSet<>(Arrays.asList(expectedKeys));
+		expect(keys);
+	}
+
+	/**
+	 * Check whether the head token is a certain type.
+	 *
+	 * @param val
+	 *        The type to check for.
+	 *
+	 * @return Whether or not the head token is of that type.
+	 */
+	public boolean headIs(final K val) {
+		return current().getKey().equals(val);
+	}
+}