impure_func_t4.m:019: In call to semipure function
impure_func_t4.m:019:   `impure_func_t4.get_counter'/0:
impure_func_t4.m:019:   purity error: call must be in an explicit unification
impure_func_t4.m:019:   which is preceded by `semipure' indicator.