diff --git a/eval/eval.go b/eval/eval.go
index 46dde742..b092a639 100644
--- a/eval/eval.go
+++ b/eval/eval.go
@@ -2,6 +2,7 @@ package eval
 
 import (
 	"fmt"
+	"io"
 	"math"
 	"os"
 	"strings"
@@ -13,11 +14,13 @@ import (
 )
 
 type State struct {
-	env *object.Environment
+	env   *object.Environment
+	Out   io.Writer
+	NoLog bool // turn log() into print() (for EvalString)
 }
 
 func NewState() *State {
-	return &State{env: object.NewEnvironment()}
+	return &State{env: object.NewEnvironment(), Out: os.Stdout}
 }
 
 // Forward to env to count the number of bindings. Used mostly to know if there are any macros.
@@ -213,10 +216,19 @@ func (s *State) evalBuiltin(node *ast.Builtin) object.Object {
 				buf.WriteString(r.Inspect())
 			}
 		}
-		if node.Type == token.PRINT {
-			os.Stdout.WriteString(buf.String())
+		doLog := node.Type != token.PRINT
+		if s.NoLog && doLog {
+			doLog = false
+			buf.WriteRune('\n') // log() has a implicit newline when using log.Xxx, print() doesn't.
+		}
+		if doLog {
+			// Consider passing the arguments to log instead of making a string concatenation.
+			log.Printf("%s", buf.String())
 		} else {
-			log.Printf(buf.String())
+			_, err := s.Out.Write([]byte(buf.String()))
+			if err != nil {
+				log.Warnf("print: %v", err)
+			}
 		}
 		return object.NULL
 	case token.FIRST:
diff --git a/repl/repl.go b/repl/repl.go
index b4072c27..c4160ec5 100644
--- a/repl/repl.go
+++ b/repl/repl.go
@@ -51,8 +51,10 @@ func EvalAll(s, macroState *eval.State, in io.Reader, out io.Writer, options Opt
 func EvalString(what string) string {
 	s := eval.NewState()
 	macroState := eval.NewState()
-	out := strings.Builder{}
-	EvalOne(s, macroState, what, &out, Options{All: true, ShowEval: true, NoColor: true})
+	out := &strings.Builder{}
+	s.Out = out
+	s.NoLog = true
+	EvalOne(s, macroState, what, out, Options{All: true, ShowEval: true, NoColor: true})
 	return out.String()
 }
 
diff --git a/repl/repl_test.go b/repl/repl_test.go
new file mode 100644
index 00000000..209418db
--- /dev/null
+++ b/repl/repl_test.go
@@ -0,0 +1,30 @@
+package repl_test
+
+import (
+	"testing"
+
+	"grol.io/grol/repl"
+)
+
+func TestEvalString(t *testing.T) {
+	s := `
+fact=func(n) { // function
+    log("called fact", n) // log (timestamped stderr output)
+    if (n<=1) {
+        return 1
+    }
+    n*fact(n-1)
+}
+result = fact(5)
+print("Factorial of 5 is", result, "\n") // print to stdout
+result`
+	expected := `called fact 5
+called fact 4
+called fact 3
+called fact 2
+called fact 1
+Factorial of 5 is 120` + " \n120\n" // there is an extra space before \n that vscode wants to remove
+	if got := repl.EvalString(s); got != expected {
+		t.Errorf("EvalString() got\n---\n%s\n---want---\n%s\n---", got, expected)
+	}
+}