2.12.3 Rationale

R5RS Scheme requires certain operations to signal an error when they fail. “Signalling an error” means that implementations must detect and report the error. Moreover, R5RS encourages, but not requires, implementations to signal an error in many more circumstances.

However, there is no direct way for the Scheme application programmer to report an error that occured in his or her own application. This means that Scheme procedures created by applications or libraries are in this respect not on equal footing with procedures provided by the Scheme system.

Many Scheme systems already provide a mechanism that allows application code to report an error. At least the following implementations support such a mechanism: Bigloo, Guile, MIT Scheme, PLT Scheme, RScheme, Scsh, SCM, all implementations supported by Slib. Of these implementations, the following have an error mechanism compatible with this SRFI: Guile, MIT Scheme, PLT Scheme, RScheme, Scsh. The implementation in Slib has a different name than the one proposed in this SRFI.

To summarise, many implementations already have the error reporting mechanism described in this SRFI and others are easily made compatible with this SRFI. This shows that the proposed mechanism is considered useful and that it is easy to implement in most major implementations.