About input argument specification

[wukefe]

Given a program with multiple parameters, such as foo (a, b), how can we pass the argument information that the arguments a and b are two vectors with the same length?

Right now, we can pass the following argument specifications which merely mean a and b are two vectors.

DOUBLE&1*?&REAL
DOUBLE&1*?&REAL

Is it useful to add the feature? Or if this feature is already available, please let me know. (PS: I have tried to replace ? with a name n, but failed to pass the compilation.)

Thanks,

Hanfeng