Semantics is also involved, because thinking has to be thinking about something. Computational functional relations are solely a matter of syntax, not semantics. So thinking is not just a matter of computational functioning. Semantics in grammar has to do with what expressions in a language mean. In this sense, the syntactical properties of expressions do not fix what they mean.
Meaning is use of syntax.
The intentionality of descriptions in words is not intrinsic to those words but derives from the intentionality of the thoughts the words express. If we changed our language, the same words would have different content. There is no way to have the same thoughts with different content. A computer calculates my bank balance. I interpret what it does as calculation.