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
---
 .../bjc/utils/patterns/MutablePatternMatcher.java  | 84 ++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 base/src/main/java/bjc/utils/patterns/MutablePatternMatcher.java

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

diff --git a/base/src/main/java/bjc/utils/patterns/MutablePatternMatcher.java b/base/src/main/java/bjc/utils/patterns/MutablePatternMatcher.java
new file mode 100644
index 0000000..7900262
--- /dev/null
+++ b/base/src/main/java/bjc/utils/patterns/MutablePatternMatcher.java
@@ -0,0 +1,84 @@
+package bjc.utils.patterns;
+
+import java.util.*;
+
+import bjc.data.*;
+
+/**
+ * A pattern matcher over a mutable set of patterns.
+ * 
+ * Note that modifying a pattern matcher while it is currently doing pattern
+ * matching is a wonderful way to cause strange behavior.
+ * 
+ * @author Ben Culkin
+ *
+ * @param <ReturnType> The type returned by the pattern matcher.
+ */
+public class MutablePatternMatcher<ReturnType, InputType>
+	implements IPatternMatcher<ReturnType, InputType>{
+	private final List<ComplexPattern<ReturnType, Object, InputType>> patterns;
+	
+	/**
+	 * Create a new mutable pattern matcher with no patterns.
+	 */
+	public MutablePatternMatcher() {
+		patterns = new ArrayList<>();
+	}
+
+	/**
+	 * Create a new mutable pattern matcher with the given set of patterns.
+	 * 
+	 * @param patterns The set of patterns to match on.
+	 */
+	@SuppressWarnings("unchecked")
+	public MutablePatternMatcher(ComplexPattern<ReturnType, ?, InputType>... patterns) {
+		this();
+		
+		for (ComplexPattern<ReturnType, ?, InputType> pattern : 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.add((ComplexPattern<ReturnType, Object, InputType>) pattern);
+		}
+	}
+	
+	@Override
+	public ReturnType matchFor(InputType input) throws NonExhaustiveMatch {
+		Iterator<ComplexPattern<ReturnType, Object, InputType>> iterator;
+		for (iterator = new NonCMEIterator<>(patterns);
+				iterator.hasNext();) {
+			ComplexPattern<ReturnType, Object, InputType> pattern = iterator.next();
+			
+			IPair<Boolean, Object> matches = pattern.matches(input);
+			
+			if (matches.getLeft()) {
+				pattern.apply(input, matches.getRight());
+			}
+		}
+
+		throw new NonExhaustiveMatch("Non-exhaustive match against " + input);
+	}
+
+	/**
+	 * Add a pattern to this pattern matcher.
+	 * 
+	 * @param pattern The pattern to add.
+	 * 
+	 * @return Whether or not the pattern was added.
+	 */
+	@SuppressWarnings("unchecked")
+	public boolean addPattern(ComplexPattern<ReturnType, ?, InputType> pattern) {
+		return patterns.add((ComplexPattern<ReturnType, Object, InputType>) pattern);
+	}
+	
+	/**
+	 * Remove a pattern from this pattern matcher.
+	 * 
+	 * @param pattern The pattern to remove.
+	 * 
+	 * @return Whether or not the pattern was removed.
+	 */
+	public boolean removePattern(ComplexPattern<ReturnType, ?, InputType> pattern) {
+		return patterns.remove(pattern);
+	}
+}
-- 
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