[jetti]

I’m not really sure how you would be able to write an interpreter without a parser, since you need to know what the user is trying to do. For a more complete tutorial there is Make-A-Lisp (mal) [0] that has steps for making a lisp in various (including JavaScript) and has a process guide [1] to get started.

[0] https://github.com/kanaka/mal

[1] https://github.com/kanaka/mal/blob/master/process/guide.md

[KineticLensman]

I can second Make-A-Lisp. I worked through it in C# initially, and I'm now halfway through a Rust implementation. The MAL process guide is a good set of instructions but doesn't go as far as actually presenting pseudocode, so you do have to think, and sometimes 'cheat' by looking at one of the reference implementations. In terms of tokenising and parsing, the MAL guide does include a monster regex statement that recognises the relevant tokens, and the parsing is quite easy due to Lisp's relatively simple syntax. If you choose the right implementation language, it will do some of the heavy lifting for you (notably memory management).

[Edit] Just wanted to reiterate that lexing/parsing Lisp is easy as per the MAL instructions. IIRC the things that I found hardest (in C#, as a C# newby) were understanding how to implement the closures required to support function definition, and then implementing Lisp's macro expansion.

[naasking]

You can create an interpreter in the finally tagless style:

https://okmij.org/ftp/tagless-final/

This embeds the target language as combinators in a host language, so you can construct and evaluate programs.

[jetti]

I have not heard of tagless final style interpreter before and that seems really neat. However, based on the link it seems that tagless final interpreter uses a strong type language like Haskell or ML so I don’t know how well it would translate to Javascript, which is what the GP comment said they were using.