[plt-scheme] detecting parameter types (contracts?)

Is there a way to automatically detect paramater types of the
primative functions?  I'm guessing not, but perhaps the "contracts"
functions have something in them.  While this example is highly
contrived, I'll present a example to be clear on what i'm looking for:

(+ (if (equal? 'number (get-type-of-parameter-1 +))
       2
       "nifty string")
   7)

or in english:
Given the function +, is there a way to automatically determine wether
i should be passing it a number, a symbol, or a string?


Corey

-- 
((lambda (y) (y y)) (lambda (y) (y y)))