[m-dev.] use of require/1 and mode error?

[Christopher Rodd SPEIRS]

> clpr/samples/laplace.m:
> 	Use an if-then-else rather than require/1, because the use
> 	of require/1 is a mode error. 
> 	(XXX the compiler doesn't yet detect the error.)
>  
> -	% XXX use of `require' is a bug (should be a mode error)
> -	{ require(laplace(X), "laplace failed\n") },


Why is the use of require a mode error?  Is the use of require always a
mode error, or is there something special about this case?

Chris