Bear set forth seven arguments in favor of type declarations.
His sixth point was:
> 6) Optionality:  Scheme systems are *NOT* required to use the information
>    available in type declarations for optimization or checking purposes.

Optional type declarations cannot possibly require all
implementations to behave similarly.  Therefore optional
type declarations cannot possibly solve the portability
and predictability problems that are the main focus of
SRFI-77.

> 7) Abstraction Barriers:  I think that implementors who care about
>    different aspects of numeric computation ought to be free to use
>    a different representation for numbers.  What the proposed "type-
>    specific numeric operations" intend to do is to mandate hardware
>    ints/floats as the representation for numbers, and if you want to
>    deal with hardware numbers, I suggest you ought to be talking about
>    an interface to machine code rather than scheme numeric operations.

I do not agree with your characterization of the intent
of the type-specific numeric operations that are described
in SRFI-77.  Furthermore I would note that those operations
do not mandate any particular representation for numbers.
To my mind, this is one of the single most important things
to understand about SRFI-77.

Will