Strings

BUP allows string only in the output block. A string could be:

An explicit string by adding quotes at the beginning and at the end of the text:
A string concat using ++ operator:
```
<string> <++ <string>>*
```
A string between parenthesis:
```
( <string> )
```
A ternary operation having a string expression to the both sides:
```
<boolExpression> : ? <string1> : <string2>
```
A variable or param access automatically casted to string. > Strings are only allowed in output block, where variables are treated as bool basic type

Variables are automatically casted to bool basic type to do operations between expressions in the output-block. - An expression result, automatically casted to string. - A list automatically casted to string.

Lists are casted to string using the format "[<expr> , <expr*>]"