[racket] TR: predicate for a Float ?

I'd like a predicate that checks whether a number is a Float. Here's what I tried:

         (: amplitudes/t (Listof Float))
         (define amplitudes/t
           (cond [(andmap inexact-real? amplitudes)
                  amplitudes]
                 [(error 'impossible "Make TR happy")]))

But I get:

Type Checker: Expected Coefficients, but got (U Null (Pairof Inexact-Real (Listof Inexact-Real))) in: amplitudes

Examining the difference between Inexact-Real and Float yields this:

> (:type Float)
(U Float-Positive-Zero Float-Negative-Zero Float-Nan Positive-Float Negative-Float)
> (:type Inexact-Real)
(U Float-Positive-Zero Float-Negative-Zero Float-Nan Positive-Float Negative-Float Single-Flonum-Positive-Zero Single-Flonum-Negative-Zero Single-Flonum-Nan Positive-Single-Flonum Negative-Single-Flonum)

...which actually made me laugh out loud.  Is there a predicate I can use instead of 'inexact-real?' that checks whether a number belongs to the type Float?


(The larger picture here is that TR *had* this type information--namely, that amplitudes is a (Listof Float), but it looks like it's getting lost by an overly-complex expansion of match.)

John

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