Add basic pattern matching

Adds a basic pattern matching implementation. Not perfect, but pretty
good, considering what we have to work with

1 files changed, 85 insertions, 0 deletions

diff --git a/base/src/main/java/bjc/utils/patterns/IPatternMatcher.java b/base/src/main/java/bjc/utils/patterns/IPatternMatcher.java
new file mode 100644
index 0000000..b688a47
--- /dev/null
+++ b/base/src/main/java/bjc/utils/patterns/IPatternMatcher.java
@@ -0,0 +1,85 @@
+package bjc.utils.patterns;
+
+import java.util.function.*;
+
+import bjc.functypes.*;
+
+/**
+ * Represents a pattern matcher against a series of patterns.
+ * 
+ * @author Ben Culkin
+ *
+ * @param <ReturnType> The type returned from matching the patterns.
+ * @param <InputType> The type to match against.
+ */
+@FunctionalInterface
+public interface IPatternMatcher<ReturnType, InputType> {
+	/**
+	 * Match an input object against a set of patterns.
+	 * 
+	 * @param input The object to match against.
+	 * 
+	 * @return The result of matching against the object.
+	 * 
+	 * @throws NonExhaustiveMatch If none of the patterns in this set match
+	 */
+	ReturnType matchFor(InputType input) throws NonExhaustiveMatch;
+	
+	/**
+	 * Create a pattern matcher against a static set of patterns.
+	 * 
+	 * @param <RetType> The type returned from matching the patterns.
+	 * @param <InpType> The type to match against.
+	 * 
+	 * @param patterns The set of patterns to match on.
+	 * 
+	 * @return A pattern matcher which matches on the given patterns.
+	 */
+	@SafeVarargs
+	static <RetType, InpType> IPatternMatcher<RetType, InpType> matchingOn(
+			ComplexPattern<RetType, ?, InpType>... patterns) {
+		return new PatternMatcher<>(patterns);
+	}
+	
+	/**
+	 * Create a pattern matcher from a handler function.
+	 * 
+	 * @param <RetType> The type returned by the matcher.
+	 * @param <InpType> The type to match against.
+	 * 
+	 * @param handler The handler function.
+	 * 
+	 * @return A pattern matcher defined by the given handler.
+	 */
+	static <RetType, InpType> IPatternMatcher<RetType, InpType> from(
+			ThrowFunction<InpType, RetType, NonExhaustiveMatch> handler) {
+		return new FunctionalPatternMatcher<>(handler);
+	}
+	
+	/**
+	 * Create a pattern matcher which applies a transform to its input.
+	 * 
+	 * @param <NewInput> The new input type to use.
+	 * @param transformer The function to convert from the new input to the old input.
+	 * 
+	 * @return A pattern matcher which takes values of the new type instead.
+	 */
+	default <NewInput> IPatternMatcher<ReturnType, NewInput> transformInput(
+			Function<NewInput, InputType> transformer) {
+		return from(inp -> matchFor(transformer.apply(inp)));
+	}
+
+	/**
+	 * Create a pattern matcher which applies a transform to its output.
+	 * 
+	 * @param <NewOutput> The new output type to use.
+	 * 
+	 * @param transformer The function to convert from the new output to the old output.
+	 * 
+	 * @return A pattern matcher which takes values of the new type instead.
+	 */
+	default <NewOutput> IPatternMatcher<NewOutput, InputType> transformOutput(
+			Function<ReturnType, NewOutput> transformer) {
+		return from(inp -> transformer.apply(matchFor(inp)));
+	}
+}
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