method eval_exp : exp -> 'r m
method eval_var : var -> 'r m
method eval_int : word -> 'r m
method eval_cast : cast -> int -> exp -> 'r m
method eval_ite : cond:exp -> yes:exp -> no:exp -> 'r m
method eval_concat : exp -> exp -> 'r m
method eval_unknown : string -> typ -> 'r m