Sort of. The parenthesis around an expression like (a b +) imply a result of some type. That type is defined by the whatever type promotion rules are in place for the operands and operators. Thus, if a and b are integers in the range -MIN_VALUE to MAX_VALUE, and + is defined as integer addition, then the 'type' implied by (a b +) is an integer in that range (or possibly an error condition, if under/overflow).

The reason you don't see a stack language that evaluates from left to right is because then it wouldn't be a stack language.