Implement ConstantPattern

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

@@ -0,0 +1,36 @@
+package it.cavallium.warppi.math.rules.dsl.patterns;
+
+import it.cavallium.warppi.math.Function;
+import it.cavallium.warppi.math.MathContext;
+import it.cavallium.warppi.math.functions.Variable;
+import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Matches and generates a specific symbolic constant.
+ */
+public class ConstantPattern extends VisitorPattern {
+	private final char symbol;
+
+	public ConstantPattern(final char symbol) {
+		this.symbol = symbol;
+	}
+
+	@Override
+	public Optional<Map<String, Function>> visit(final Variable variable) {
+		if (variable.getType().equals(Variable.V_TYPE.CONSTANT)
+				&& variable.getChar() == symbol) {
+			return Optional.of(new HashMap<>());
+		} else {
+			return Optional.empty();
+		}
+	}
+
+	@Override
+	public Function replace(final MathContext mathContext, final Map<String, Function> subFunctions) {
+		return new Variable(mathContext, symbol, Variable.V_TYPE.CONSTANT);
+	}
+}

core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java

@@ -2,6 +2,7 @@ package it.cavallium.warppi.math.rules.dsl;
 
 import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
+import it.cavallium.warppi.math.MathematicalSymbols;
 import it.cavallium.warppi.math.functions.*;
 import it.cavallium.warppi.math.functions.Number;
 import it.cavallium.warppi.math.functions.equations.Equation;
@@ -188,6 +189,27 @@ public class PatternTest {
 		assertEquals(rootSquare, replacement);
 	}
 
+	@Test
+	public void constantPattern() {
+		final Pattern pattern = new ConstantPattern(MathematicalSymbols.PI);
+
+		final Function shouldNotMatch = new Variable(
+				mathContext,
+				MathematicalSymbols.EULER_NUMBER,
+				Variable.V_TYPE.CONSTANT
+		);
+		assertFalse(pattern.match(shouldNotMatch).isPresent());
+
+		final Function shouldMatch = new Variable(
+				mathContext,
+				MathematicalSymbols.PI,
+				Variable.V_TYPE.CONSTANT
+		);
+		final Optional<Map<String, Function>> subFunctions = pattern.match(shouldMatch);
+		assertTrue(subFunctions.isPresent());
+		assertEquals(shouldMatch, pattern.replace(mathContext, subFunctions.get()));
+	}
+
 	@Test
 	public void otherBinaryPatterns() {
 		final Number one = new Number(mathContext, 1);