tylr

tylr is a tiny tile-based editor, a new kind of structure editor that, like a text editor, supports linear token-level editing workflows but, unlike a text editor, ensures your manipulated tokens can always be parsed back into a well-formed abstract syntax tree (AST).

Other structure editors restrict you to simple operations on the AST. For example, if you have the expression 2 + 3 * 4 in Scratch or MPS, you can't select things like * 4 or even 2 + 3—never mind directly manipulate them—because they don't correspond to complete subtrees in the AST. Uniquely among structure editors, tylr lets you select and manipulate near-arbitrary range selections, including those corresponding to sub- and cross-tree portions of the AST.

You can play with a running instance of this code at tylr.fun. Click on the help button in the upper-right corner for a gif-laden Twitter thread on how it works.

Building and running tylr locally

Install OPAM version ≥2.0 and use it to install OCaml 4.08.1 as described here.

Clone this repo, run the following commands in the root directory, and paste the output of the final command into your browser address bar.

make deps       # build dependencies (locked in opam.export)
make            # build tylr src
make echo-html  # echo path to compiled page