DSL EXPRESSION:
$x = $a + $b + $c


AST:
"block" [tt:block] [nt:StatementBlock]
    "=" [tt:equals] [nt:Assignment]
        "$x" [tt:field_name] [nt:DirectFieldValue]
        "+" [tt:op_plus] [nt:Operator]
            "+" [tt:op_plus] [nt:Operator]
                "$a" [tt:field_name] [nt:DirectFieldValue]
                "$b" [tt:field_name] [nt:DirectFieldValue]
            "$c" [tt:field_name] [nt:DirectFieldValue]

