added in_slime_chunk, seed, add seed option to rand

src/main/java/carpet/script/Expression.java

@@ -2720,12 +2720,15 @@ public class Expression
      * length('foo') => 3
      * </pre>
      *
-     * <h3><code>rand(expr)</code></h3>
+     * <h3><code>rand(expr), rand(expr, seed)</code></h3>
      * <p>returns a random number from <code>0.0</code>
      * (inclusive) to <code>expr</code> (exclusive).
      * In boolean context (in conditions, boolean functions, or <code>bool</code>), returns
      * false if the randomly selected value is less than 1. This means that <code>rand(2)</code> returns true half
-     * of the time and <code>rand(5)</code> returns true for 80% (4/5) of the time</p>
+     * of the time and <code>rand(5)</code> returns true for 80% (4/5) of the time. If seed is not provided, uses a random seed.
+     * If seed is provided, each consecutive call to rand() will act like 'next' call to the same random object.
+     * Scarpet keeps track of up to 1024 custom random number generators, so if you exceed this number (per app), then your
+     * random sequence will revert to the beginning.</p>
      * <pre>
      * map(range(10), floor(rand(10))) =&gt; [5, 8, 0, 6, 9, 3, 9, 9, 1, 8]
      * map(range(10), bool(rand(2))) =&gt; [1, 1, 1, 0, 0, 1, 1, 0, 0, 0]
@@ -2982,7 +2985,12 @@ public class Expression
         addUnaryFunction("type", v -> new StringValue(v.getTypeString()));
 
         addUnaryFunction("length", v -> new NumericValue(v.length()));
-        addLazyFunction("rand", 1, (c, t, lv) -> {
+        addLazyFunction("rand", -1, (c, t, lv) -> {
+            int argsize = lv.size();
+            Random randomizer = Expression.randomizer;
+            if (argsize != 1 && argsize != 2)
+                throw new InternalExpressionException("'rand' takes one (range) or two arguments (range and seed)");
+            if (argsize == 2) randomizer = c.host.getRandom(NumericValue.asNumber(lv.get(1).evalValue(c)).getLong());
             Value argument = lv.get(0).evalValue(c);
             if (argument instanceof ListValue)
             {