diff --git a/cue/ast.go b/cue/ast.go
index e1303ea..9dbed65 100644
--- a/cue/ast.go
+++ b/cue/ast.go
@@ -85,6 +85,10 @@
 
 func newVisitor(idx *index, inst *build.Instance, obj, resolveRoot *structLit) *astVisitor {
 	ctx := idx.newContext()
+	return newVisitorCtx(ctx, inst, obj, resolveRoot)
+}
+
+func newVisitorCtx(ctx *context, inst *build.Instance, obj, resolveRoot *structLit) *astVisitor {
 	v := &astVisitor{
 		object: obj,
 	}
diff --git a/cue/builtin.go b/cue/builtin.go
index daaaae0..b6fdd17 100644
--- a/cue/builtin.go
+++ b/cue/builtin.go
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 //go:generate go run gen.go
+//go:generate goimports -w builtins.go
 
 package cue
 
@@ -366,8 +367,9 @@
 		return v
 	case nil:
 		return &nullLit{src.base()}
-	case *Instance:
-		return v.eval(ctx)
+	case ast.Expr:
+		x := newVisitorCtx(ctx, nil, nil, nil)
+		return ctx.manifest(x.walk(v))
 	case error:
 		return ctx.mkErr(src, v.Error())
 	case bool:
diff --git a/cue/builtins.go b/cue/builtins.go
index 62a0ed0..f16d702 100644
--- a/cue/builtins.go
+++ b/cue/builtins.go
@@ -371,7 +371,7 @@
 
 					return nil, fmt.Errorf("json: could not parse JSON: %v", err)
 				}
-				return FromExpr(fset, expr)
+				return expr, nil
 			}()
 		},
 	}},
@@ -420,11 +420,7 @@
 			data := c.bytes(0)
 			c.ret, c.err = func() (interface{}, error) {
 				fset := token.NewFileSet()
-				expr, err := yaml.Unmarshal(fset, "", data)
-				if err != nil {
-					return nil, err
-				}
-				return FromExpr(fset, expr)
+				return yaml.Unmarshal(fset, "", data)
 			}()
 		},
 	}},
diff --git a/pkg/encoding/json/manual.go b/pkg/encoding/json/manual.go
index 9b2d324..3af3d37 100644
--- a/pkg/encoding/json/manual.go
+++ b/pkg/encoding/json/manual.go
@@ -20,6 +20,7 @@
 	"fmt"
 
 	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/ast"
 	"cuelang.org/go/cue/parser"
 	"cuelang.org/go/cue/token"
 )
@@ -90,7 +91,7 @@
 }
 
 // Unmarshal parses the JSON-encoded data.
-func Unmarshal(b []byte) (*cue.Instance, error) {
+func Unmarshal(b []byte) (ast.Expr, error) {
 	if !json.Valid(b) {
 		return nil, fmt.Errorf("json: invalid JSON")
 	}
@@ -100,5 +101,5 @@
 		// NOTE: should never happen.
 		return nil, fmt.Errorf("json: could not parse JSON: %v", err)
 	}
-	return cue.FromExpr(fset, expr)
+	return expr, nil
 }
diff --git a/pkg/encoding/yaml/manual.go b/pkg/encoding/yaml/manual.go
index c4e609a..646e7aa 100644
--- a/pkg/encoding/yaml/manual.go
+++ b/pkg/encoding/yaml/manual.go
@@ -18,6 +18,7 @@
 	"bytes"
 
 	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/ast"
 	"cuelang.org/go/cue/token"
 	"cuelang.org/go/internal/third_party/yaml"
 	goyaml "github.com/ghodss/yaml"
@@ -51,11 +52,7 @@
 }
 
 // Unmarshal parses the YAML to a CUE instance.
-func Unmarshal(data []byte) (*cue.Instance, error) {
+func Unmarshal(data []byte) (ast.Expr, error) {
 	fset := token.NewFileSet()
-	expr, err := yaml.Unmarshal(fset, "", data)
-	if err != nil {
-		return nil, err
-	}
-	return cue.FromExpr(fset, expr)
+	return yaml.Unmarshal(fset, "", data)
 }