feat(logic): add crypto_hash/2 predicate

x/logic/interpreter/registry.go

@@ -115,6 +115,7 @@ var Registry = map[string]RegistryEntry{
 	"bank_spendable_balances/2": {predicate.BankSpendableBalances, 1},
 	"bank_locked_balances/2":    {predicate.BankLockedBalances, 1},
 	"did_components/2":          {predicate.DIDComponents, 1},
+	"crypto_hash/2":             {predicate.CryptoHash, 1},
 }
 
 // RegistryNames is the list of the predicate names in the Registry.

x/logic/predicate/crypto.go

@@ -0,0 +1,22 @@
+package predicate
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/ichiban/prolog/engine"
+	"github.com/tendermint/tendermint/crypto"
+)
+
+func CryptoHash(vm *engine.VM, data, hash engine.Term, cont engine.Cont, env *engine.Env) *engine.Promise {
+	return engine.Delay(func(ctx context.Context) *engine.Promise {
+		switch d := env.Resolve(data).(type) {
+		case engine.Atom:
+			result := crypto.Sha256([]byte(d.String()))
+			return engine.Unify(vm, hash, engine.NewAtom(hex.EncodeToString(result)), cont, env)
+		default:
+			return engine.Error(fmt.Errorf("crypto_hash/2: cannot unify %s from %s", data, hash))
+		}
+	})
+}