Function Return Values - SBCL 1.0.31 User Manual
Description: SBCL 1.0.31 User Manual

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#### 16.3.4 Function Return Values

The return value is usually the same as for the C binding, except in error cases: where the C function is defined as returning some sentinel value and setting `errno` on error, we instead signal an error of type `SYSCALL-ERROR`. The actual error value (`errno`) is stored in this condition and can be accessed with `SYSCALL-ERRNO`.

We do not automatically translate the returned value into “Lispy” objects – for example, `SB-POSIX:OPEN` returns a small integer, not a stream. Exception: boolean-returning functions (or, more commonly, macros) do not return a C integer, but instead a Lisp boolean.