Define the Pattern interface and its core methods

core/src/main/java/it/cavallium/warppi/math/rules/dsl/Pattern.java

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+package it.cavallium.warppi.math.rules.dsl;
+
+import it.cavallium.warppi.math.Function;
+
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Recognizes and generates functions of some specific shape.
+ */
+public interface Pattern {
+    /**
+     * Tries to match this pattern against a function and capture sub-functions.
+     *
+     * @param function The function to test the pattern against.
+     * @return The captured sub-functions, or an empty <code>Optional</code> if
+     *         the pattern doesn't match.
+     */
+    Optional<Map<String, Function>> match(Function function);
+
+    /**
+     * Creates a new function by filling in sub-functions within this pattern.
+     *
+     * @param subFunctions A map of named sub-functions to be inserted into this pattern.
+     * @return The resulting function.
+     */
+    Function replace(Map<String, Function> subFunctions);
+}