re-implement indexOf simplify()

Author: sovdeeth

src/main/java/ch/njol/skript/expressions/ExprIndicesOf.java

@@ -1,7 +1,7 @@
 package ch.njol.skript.expressions;
 
-import ch.njol.skript.lang.SyntaxStringBuilder;
-import ch.njol.skript.lang.Variable;
+import ch.njol.skript.lang.*;
+import ch.njol.skript.lang.simplification.SimplifiedLiteral;
 import ch.njol.skript.util.LiteralUtils;
 import ch.njol.util.Pair;
 import org.bukkit.event.Event;
@@ -12,8 +12,6 @@
 import ch.njol.skript.doc.Examples;
 import ch.njol.skript.doc.Name;
 import ch.njol.skript.doc.Since;
-import ch.njol.skript.lang.Expression;
-import ch.njol.skript.lang.ExpressionType;
 import ch.njol.skript.lang.SkriptParser.ParseResult;
 import ch.njol.skript.lang.util.SimpleExpression;
 import ch.njol.util.Kleenean;
@@ -221,6 +219,16 @@ public Class<?> getReturnType() {
 		return String.class;
 	}
 
+	@Override
+	public Expression<?> simplify() {
+		if (this.position && this.string
+			&& value instanceof Literal<?> && objects instanceof Literal<?>
+		) {
+			return SimplifiedLiteral.fromExpression(this);
+		}
+		return this;
+	}
+
 	@Override
 	public String toString(@Nullable Event event, boolean debug) {
 		SyntaxStringBuilder builder = new SyntaxStringBuilder(event, debug);