Import all classes

src/main/java/de/plugh/compositeparse/parsers/Decision.java

@@ -0,0 +1,66 @@
+package de.plugh.compositeparse.parsers;
+
+import de.plugh.compositeparse.Block;
+import de.plugh.compositeparse.Pair;
+import de.plugh.compositeparse.ParseException;
+import de.plugh.compositeparse.Parser;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Function;
+
+/**
+ * Decide which parser to use from a list of "body" parsers and their "head"s.
+ * <p>
+ * If a "head" parses successfully, the corresponding "body" parser must be successful, otherwise a parse exception is
+ * raised. If no "head" is successful, the {@link Decision} parser fails too.
+ *
+ * @param <T> return type of the parser
+ */
+public class Decision<T> implements Parser<T> {
+
+    private final List<Pair<Parser<?>, Parser<T>>> pairs;
+
+    /**
+     * Create a new {@link Decision} parser from all passed arguments, which are "head"-"body" pairs.
+     *
+     * @param pairs multiple "head"-"body" pairs
+     */
+    @SafeVarargs
+    public Decision(Pair<Parser<?>, Parser<T>>... pairs) {
+        this.pairs = new ArrayList<>();
+        for (Pair<Parser<?>, Parser<T>> pair : pairs) {
+            this.pairs.add(pair);
+        }
+    }
+
+    /**
+     * Create a new {@link Decision} parser from a list of "head"-"body" pairs.
+     *
+     * @param pairs a list of "head"-"body" pairs
+     */
+    public Decision(List<Pair<Parser<?>, Parser<T>>> pairs) {
+        this.pairs = new ArrayList<>(pairs);
+    }
+
+    @Override
+    public Function<List<Block>, String> getNamingScheme() {
+        return Block::alternative;
+    }
+
+    @Override
+    public T read(Block block) throws ParseException {
+        for (Pair<Parser<?>, Parser<T>> pair : pairs) {
+            try {
+                pair.getFirst().parse(block);
+            } catch (ParseException e) {
+                continue;
+            }
+
+            return pair.getSecond().parse(block);
+        }
+
+        throw new ParseException(block);
+    }
+
+}