Next: , Previous: Non-immediate Datatypes, Up: How Guile does it

A.2.6 Signalling Type Errors

Every function visible at the Scheme level should aggressively check the types of its arguments, to avoid misinterpreting a value, and perhaps causing a segmentation fault. Guile provides some macros to make this easier.

— Macro: void SCM_ASSERT (int test, SCM obj, unsigned int position, const char *subr)

If test is zero, signal a “wrong type argument” error, attributed to the subroutine named subr, operating on the value obj, which is the position'th argument of subr.

— Macro: int SCM_ARG1
— Macro: int SCM_ARG2
— Macro: int SCM_ARG3
— Macro: int SCM_ARG4
— Macro: int SCM_ARG5
— Macro: int SCM_ARG6
— Macro: int SCM_ARG7

One of the above values can be used for position to indicate the number of the argument of subr which is being checked. Alternatively, a positive integer number can be used, which allows to check arguments after the seventh. However, for parameter numbers up to seven it is preferable to use SCM_ARGN instead of the corresponding raw number, since it will make the code easier to understand.

— Macro: int SCM_ARGn

Passing a value of zero or SCM_ARGn for position allows to leave it unspecified which argument's type is incorrect. Again, SCM_ARGn should be preferred over a raw zero constant.