3 ms·

Lisp user here. How come they can’t change their parser?

goto11 3y ago
The describe it as "an unsanctioned hack on top of typescript", so I think the point is they don't want to change the typescript parser itself, but provide this as an add-on.
tonyg 3y ago
The implementation of the parser is deeply, deeply baked in to the whole of the MS TypeScript compiler and tooling libraries. It's not feasible to, e.g., add new AST nodes, or change or augment the grammar producing them, and there's nothing like S- or D-expressions to allow for read/parse separation like in lisps. (Which is why I added something D-expression like.)
o1y32 3y ago
Practically speaking, the TS team wants the language to resemble JS as much as possible and usually avoids completely new syntax, e.g. new expressions. For this reason they haven't added switch expressions even though technically it's probably not hard to do.
- jsmith45 3y ago
  yeah, at this point, other than type annotations and other type related syntax (like type imports and type declarations), the team mostly view the other differences from Javascript as a historical mistake. Ideally, a transpiler that does not want to type check the code, should merely need to know the syntax for type related code and strip them out. This is especially true if targeting a sufficiently recent version of ECMAScript, or if the transpiler will be doing its own transformation of newer features to older ones for backward compatibility. In practice while many typescript features can be handled like that, even some that are not strictly type features (like method accessibility modifiers), some existing features like enums needs to generate new code, although at least for that one it is an easy pattern to generate. This is especially true of any feature that cannot be made into a trivial re-write or strip rule. Namespaces and const enums are an example of features now discouraged, as simple rewriting engines cannot handle them. Indeed the whole "isolatedModules" compiler flag is specifically about making such separate simple transpilation possible, and its documentation details other scenarios that can be a problem.

The describe it as "an unsanctioned hack on top of typescript", so I think the point is they don't want to change the typescript parser itself, but provide this as an add-on.

tonyg 3y ago

The implementation of the parser is deeply, deeply baked in to the whole of the MS TypeScript compiler and tooling libraries. It's not feasible to, e.g., add new AST nodes, or change or augment the grammar producing them, and there's nothing like S- or D-expressions to allow for read/parse separation like in lisps. (Which is why I added something D-expression like.)

o1y32 3y ago

Practically speaking, the TS team wants the language to resemble JS as much as possible and usually avoids completely new syntax, e.g. new expressions. For this reason they haven't added switch expressions even though technically it's probably not hard to do.

jsmith45 3y ago
yeah, at this point, other than type annotations and other type related syntax (like type imports and type declarations), the team mostly view the other differences from Javascript as a historical mistake. Ideally, a transpiler that does not want to type check the code, should merely need to know the syntax for type related code and strip them out. This is especially true if targeting a sufficiently recent version of ECMAScript, or if the transpiler will be doing its own transformation of newer features to older ones for backward compatibility. In practice while many typescript features can be handled like that, even some that are not strictly type features (like method accessibility modifiers), some existing features like enums needs to generate new code, although at least for that one it is an easy pattern to generate. This is especially true of any feature that cannot be made into a trivial re-write or strip rule. Namespaces and const enums are an example of features now discouraged, as simple rewriting engines cannot handle them. Indeed the whole "isolatedModules" compiler flag is specifically about making such separate simple transpilation possible, and its documentation details other scenarios that can be a problem.