Add RandomFunction and seed variable

src/main/java/com/dfsek/terra/math/RandomFunction.java

@@ -0,0 +1,30 @@
+package com.dfsek.terra.math;
+
+import org.polydev.gaea.util.FastRandom;
+import parsii.eval.Expression;
+import parsii.eval.Function;
+
+import java.util.List;
+
+/**
+ * Provides access to a PRNG ({@link org.polydev.gaea.util.FastRandom})
+ * <p>
+ * Takes 1 argument, which sets the seed
+ */
+public class RandomFunction implements Function {
+    @Override
+    public int getNumberOfArguments() {
+        return 1;
+    }
+
+    @Override
+    public double eval(List<Expression> list) {
+        long seed = (long) list.get(0).evaluate();
+        return new FastRandom(seed).nextDouble();
+    }
+
+    @Override
+    public boolean isNaturalFunction() {
+        return true;
+    }
+}