feat(logic): add chain_id/1 predicate

x/logic/predicate/chain.go

@@ -0,0 +1,24 @@
+package predicate
+
+import (
+	"context"
+
+	"github.com/ichiban/prolog/engine"
+)
+
+// ChainID is higher order function that given a context returns the following predicate:
+//
+//	chain_id(?ChainID)
+//
+// where ChainID represents the current chain ID at the time of the query.
+// The predicate is deterministic, producing the same chain ID each time it is called.
+func ChainID(ctx context.Context) engine.Predicate1 {
+	return func(vm *engine.VM, chainID engine.Term, cont engine.Cont, env *engine.Env) *engine.Promise {
+		sdkContext, err := UnwrapSDKContext(ctx)
+		if err != nil {
+			return engine.Error(err)
+		}
+
+		return engine.Unify(vm, chainID, engine.CharList(sdkContext.ChainID()), cont, env)
+	}
+}