Add multi-catch to try block

docs/scarpet/language/FunctionsAndControlFlow.md

@@ -234,13 +234,17 @@ returns everywhere, but it would often lead to a messy code.
 
 It terminates entire program passing `expr` as the result of the program execution, or null if omitted.
 
-### `try(expr, id_filter?, catch_expr(_, _msg)?)`
+### `try(expr, id_filter?, catch_expr(_, _msg)?, id_filter2?, catch_expr2(_, _msg), ...)`
 
 `try` function evaluates expression, and continues further unless an exception is thrown anywhere inside `expr`, 
 it being produced by `throw` or a catchable exception being thrown by Carpet. In that case the `catch_expr` is evaluated with 
 `_` set to the id of the exception and `_msg` set to the exception message. If an `id_filter` is present, only exceptions
-with an id equal to that value will be caught, and any other exception will continue up the stack. It is recommended to filter
-the exceptions to catch to be able to distinguish from an exception that is known that may happen from one that shouldn't.
+with an id equal to that value will be caught, and any other exception will continue up the stack. You can specify multiple filters
+and their respective `catch_expr` to be able to catch different exceptions within the same code. When an exception occurs, the script 
+will try to find an equality with every provided filter in order. Therefore, even if the caught exception matches multiple filters, only 
+the first matching block will be executed. It is recommended to filter the exceptions to catch to be able to distinguish from an exception 
+that is known that may happen from one that shouldn't.
+
 This mechanic accepts skipping catch expression - then try returns `null`. This mechanism allows to terminate large 
 portion of a convoluted call stack and continue program  execution.
 

src/main/java/carpet/script/language/ControlFlow.java

@@ -76,20 +76,34 @@ public class ControlFlow {
                     throw ret;
                 if (lv.size() == 1)
                     return (c_, t_) -> Value.NULL;
+                // This is outside since it is also used in try(expr,catch_expr).
                 LazyValue __ = c.getVariable("_");
                 c.setVariable("_", (__c, __t) -> ret.exception.getValue().reboundedTo("_"));
                 LazyValue __msg = c.getVariable("_msg");
                 c.setVariable("_msg", (__c, __t) -> StringValue.of(ret.message).reboundedTo("_msg"));
-                Value val;
-                if (lv.size() == 3)
+                Value val = null; // This is always assigned, just the compiler doesn't know
+                if (lv.size() >= 3)
                 {
-                    if (!ret.exception.isInstance(lv.get(1).evalValue(c)))
+                    if (lv.size() % 2 == 0)
+                        throw new InternalExpressionException("Multi-catch block needs a catch expression for every filter");
+                    int pointer = 1;
+                    boolean handled = false;
+                    while (pointer < lv.size() -1)
+                    {
+                        if (ret.exception.isInstance(lv.get(pointer).evalValue(c)))
+                        {
+                            val = lv.get(pointer + 1).evalValue(c, t);
+                            handled = true;
+                            break;
+                        }
+                        pointer += 2;
+                    }
+                    if (!handled)
                     {
                     	c.setVariable("_", __);
                         c.setVariable("_msg", __msg);
                         throw ret;
                     }
-                    val = lv.get(2).evalValue(c, t);
                 }
                 else
                 {
@@ -97,7 +111,8 @@ public class ControlFlow {
                 }
                 c.setVariable("_",__);
                 c.setVariable("_msg", __msg);
-                return (c_, t_) -> val;
+                Value retval = val;
+                return (c_, t_) -> retval;
             }
         });
     }