Add lazy variables

src/redempt/crunch/functional/EvaluationEnvironment.java

@@ -2,11 +2,13 @@
 
 import redempt.crunch.data.CharTree;
 import redempt.crunch.token.Constant;
+import redempt.crunch.token.LazyVariable;
 import redempt.crunch.token.Operator;
 import redempt.crunch.token.Token;
 import redempt.crunch.Variable;
 
 import java.util.Locale;
+import java.util.function.DoubleSupplier;
 import java.util.function.ToDoubleFunction;
 
 /**
@@ -57,6 +59,15 @@ public void addFunctions(Function... functions) {
 		}
 	}
 
+	/**
+	 * Adds a lazily-evaluated variable that will not need to be passed with the variable values
+	 * @param name The name of the lazy variable
+	 * @param supply A function to supply the value of the variable when needed
+	 */
+	public void addLazyVariable(String name, DoubleSupplier supply) {
+		namedTokens.set(name, new LazyVariable(name, supply));
+	}
+
 	public void setVariableNames(String... names) {
 		for (int i = 0; i < names.length; i++) {
 			namedTokens.set(names[i], new Variable(null, i));

src/redempt/crunch/token/LazyVariable.java

@@ -0,0 +1,35 @@
+package redempt.crunch.token;
+
+import java.util.function.DoubleSupplier;
+
+public class LazyVariable implements Value {
+
+	private String name;
+	private DoubleSupplier supplier;
+
+	public LazyVariable(String name, DoubleSupplier supplier) {
+		this.name = name;
+		this.supplier = supplier;
+	}
+
+	@Override
+	public TokenType getType() {
+		return TokenType.LITERAL_VALUE;
+	}
+
+	@Override
+	public double getValue() {
+		return supplier.getAsDouble();
+	}
+
+	@Override
+	public Value getClone() {
+		return this;
+	}
+
+	@Override
+	public String toString() {
+		return name;
+	}
+
+}

test/redempt/crunch/test/CrunchTest.java

@@ -102,9 +102,17 @@ public void implicitMultiplicationTest() {
 	}
 
 	@Test
-	public void rootingTest(){
+	public void rootingTest() {
 		assertEquals(2, Crunch.evaluateExpression("sqrt(4)"), "Square Rooting");
 		assertEquals(2, Crunch.evaluateExpression("cbrt(8)"), "Cube Rooting");
 	}
 
+	@Test
+	public void lazyVariableTest() {
+		EvaluationEnvironment env = new EvaluationEnvironment();
+		env.addLazyVariable("x", () -> 2);
+		env.addLazyVariable("y", () -> 7);
+		assertEquals(14, Crunch.compileExpression("xy", env).evaluate());
+	}
+
 }