error -- raise an error and terminate your program

error "Wrong, wrong, wrong!!"

Produces the same kind or error messages, that yab itself produces (e.g. in case of a syntax-error). The single argument is issued along with the current line-number.

input "Please enter a number between 1 and 10: " a 
if (a<1 or a>10) error "Oh no ..." 

This program is very harsh in checking the users input; instead of just asking again, the program terminates with an error, if the user enters something wrong.
The error message would look like this:


---Error in t.yab, line 2: Oh no ... 
---Error: Program stopped due to an error