Simply using the REPL isn't a subsitute, but I would claim REPL based development is a subsitute for TDD. You are actively using the REPL to build up a solution rather than tests. Tests are written afterwards when you have a solution developed in the REPL.

The REPL is serving the same purpose as a test in TDD. REPL based development involves constant testing in the REPL as you develop a solution rather than evaluating against a formally written test on each iteration as in TDD.