Error Function

We can also make use of strings to add in an error reporting function. This can take as input a user supplied string and provide it as an error message for lval_err.

lval* builtin_error(lenv* e, lval* a) {
  LASSERT_NUM("error", a, 1);
  LASSERT_TYPE("error", a, 0, LVAL_STR);
  /* Construct Error from first argument */
  lval* err = lval_err(a->cell[0]->str);
  /* Delete arguments and return */
  lval_del(a);
  return err;
}

The final step is to register these as builtins. Now finally we can start building up libraries and writing them to files.

/* String Functions */
lenv_add_builtin(e, "load",  builtin_load);
lenv_add_builtin(e, "error", builtin_error);
lenv_add_builtin(e, "print", builtin_print);

lispy> print "Hello World!"
"Hello World!"
()
lispy> error "This is an error"
Error: This is an error
lispy> load "hello.lspy"
"Hello World!"
()
lispy>