[owl57]

Is the second one less of a program than (frobnicate "foo")? Looks about the same to me: a program that crashes unless we (define frobnicate …) first.

[Blikkentrekker]

Crashes? in most cases simply does not compile because Scheme has static scope; it is thus not a program.

But, we can of course go even further than that:

   (library (main constants (0 0 1))
     (export pi)
     (define pi 3.1415926535)
   )

`(0 0 1)` is not a valid Scheme program, no matter what one define at any point; an integer can never be the operand of an expression.