It is probably because (tokens) is allowed to have one of these types. STOKES, STOKESX, STOKEN, STOKES.
The possible position of inline data declarations are listed here and scan is not one of them.
http://help.sap.com/abapdocu_740/en/abendeclaration_positions.htm
Documentation also says data type of the variable is determined by the operand type.
In this case, operand type is not fixed, I believe.