Programming Praxis

Many programming languages are interactive, with their primary interface a read-eval-print loop. Scheme is like that, so is Python, and so is the primary language I use in my day job, Oracle SQL*Plus, and so too are many other languages.

One feature many of those languages share is a way to edit files from the REPL. For instance, in SQL*Plus, the most recently-entered command is available in a buffer, and if you say “edit” the buffer will be loaded into whatever $EDITOR you specified, so you can modify the command as needed; when the editor returns, the modified buffer is then executed.

Although Scheme doesn’t provide such an editing feature, I have been using my own for years. It’s very simple, less than a dozen lines of code, and greatly enhances my productivity.

Your task is to write an editing interface for your favorite REPL. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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