SIGNATURE SafeNat

IMPORT Nat ONLY nat
IMPORT Seq[safeNat] ONLY seq
IMPORT Seq[nat] ONLY seq

TYPE safeNat == ok (value : nat)
                error (message : denotation)

FUN ` : safeNat -> denotation
FUN safePred : safeNat -> safeNat
FUN safeSucc : safeNat -> safeNat
FUN safeLift : (nat->nat)**(nat->bool)**denotation->safeNat->safeNat
FUN safeLift2 : (nat**nat->nat)**(nat**nat->bool)**denotation->safeNat**safeNat->safeNat
FUN safeAdd : safeNat**safeNat -> safeNat
FUN safeSub : safeNat**safeNat -> safeNat
FUN safeMult : safeNat**safeNat -> safeNat
FUN safeDiv : safeNat**safeNat -> safeNat
FUN safeMap : (nat->nat)**(nat->bool)**denotation->seq[safeNat]->seq[safeNat]