From 4c0f972c4616eb549a098c3ef40d527eb542d7a6 Mon Sep 17 00:00:00 2001
From: Ben Culkin <scorpress@gmail.com>
Date: Sat, 21 Nov 2020 16:51:04 -0500
Subject: Add basic pattern matching

Adds a basic pattern matching implementation. Not perfect, but pretty
good, considering what we have to work with
---
 .../java/bjc/utils/patterns/PatternMatcher.java    | 41 ++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 base/src/main/java/bjc/utils/patterns/PatternMatcher.java

(limited to 'base/src/main/java/bjc/utils/patterns/PatternMatcher.java')

diff --git a/base/src/main/java/bjc/utils/patterns/PatternMatcher.java b/base/src/main/java/bjc/utils/patterns/PatternMatcher.java
new file mode 100644
index 0000000..e2ae9f6
--- /dev/null
+++ b/base/src/main/java/bjc/utils/patterns/PatternMatcher.java
@@ -0,0 +1,41 @@
+package bjc.utils.patterns;
+
+import bjc.data.*;
+
+/**
+ * Implements pattern-matching (of a sort) against a collection of patterns.
+ * 
+ * @author Ben Culkin
+ * 
+ * @param <ReturnType> The type returned by the pattern.
+ */
+public class PatternMatcher<ReturnType, InputType>
+	implements IPatternMatcher<ReturnType, InputType> {
+	private final ComplexPattern<ReturnType, Object, InputType>[] patterns;
+	
+	/**
+	 * Create a new pattern matcher.
+	 * 
+	 * @param patterns The set of patterns to match against.
+	 */
+	@SuppressWarnings("unchecked")
+	@SafeVarargs
+	public PatternMatcher(ComplexPattern<ReturnType, ?, InputType>...patterns) {
+		// Note: this may seem a somewhat questionable cast, but because we never
+		// actually do anything with the value who has a type matching the second
+		// parameter, this should be safe
+		this.patterns = (ComplexPattern<ReturnType, Object, InputType>[]) patterns;
+	}
+
+	@Override
+	public ReturnType matchFor(InputType input) throws NonExhaustiveMatch {
+		for (ComplexPattern<ReturnType, Object, InputType> pattern : patterns) {
+			IPair<Boolean, Object> matches = pattern.matches(input);
+			if (matches.getLeft()) {
+				pattern.apply(input, matches.getRight());
+			}
+		}
+		
+		throw new NonExhaustiveMatch("Non-exhaustive match against " + input);
+	}
+}
-- 
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