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Aubrey Jaffer <agj@xxxxxxxxxxxx> writes: > To first order: > > (define (precision-of x) (string-length (number->string x))) > > R5RS requires all numbers to have external representations; and it > specifies the allowed formats. What? number->string does not specify the allowed formats for exact numbers, only for inexact (and only for some inexact numbers at that). This isn't an accident; it was done specifically for just this reason, to allow for different representations. See the Rationale: "The unspecified case allows for infinities, NaNs, and non-flonum representations." So if X is an exact version of sqrt 2, it's perfectly fine for number->string to return anything that string->number can understand. Thomas