there’s a good write up on this somewhere that you’ll have to forgive me not being able to find tonight on mobile. In general, we want the wat syntax to mirror the binary format very closely, but that’s often at odds with a surface syntax that promotes good software engineering or good developer ux. Two cases for that off the top of my head:
* the component model wat can represent interfaces, but it can’t represent the composition of interfaces, e.g. if we were writing a new interface which opened something file-like and wanted to reuse the oflags type from wasi-filesystem, there would be no way to express that indirectly because we insist wasm binaries are self contained (don’t require you to load other resources), so the oflags type definition would need to be copied in literally.
* when we add resource types back to wit syntax (you can rewind history in wit-bindgen 2 months to find examples, we got rid of them because they were a strawman and now something quite similar is getting speced) it’s nice to have wit syntax appear just like constructors and methods, even if we all know a method desugars to a functions that take a resource as it’s first parameter in the canonical abi. It’s nice to have a distinction in wit that can be used by code generators for creating idiomatic C++, Rust, JS etc methods. Even if we give methods a faithful wat/binary repr (like, e.g. flag types, which are a shorthand for a struct full of bools), the wat/binary form will necessarily have much worse syntax than the wit will, and we think having a syntax that doesn’t send you rubbing your temples reading the component model spec will help adoption.
Speaking as someone who has had to read and write a nontrivial amount of wat over the last 5 years, it’s lovely for small examples and it’s pretty challenging for large, “real world” programs.
Got it. My concern is just fragmentation of compiler/parser tooling in order to also support wit and may introduce compatibility burden to maintain (I know wasm<->wat is 1:1, not sure about wit). However, I'm looking forward to compiling my toy lang to WASI once its MVP is solid.
* the component model wat can represent interfaces, but it can’t represent the composition of interfaces, e.g. if we were writing a new interface which opened something file-like and wanted to reuse the oflags type from wasi-filesystem, there would be no way to express that indirectly because we insist wasm binaries are self contained (don’t require you to load other resources), so the oflags type definition would need to be copied in literally.
* when we add resource types back to wit syntax (you can rewind history in wit-bindgen 2 months to find examples, we got rid of them because they were a strawman and now something quite similar is getting speced) it’s nice to have wit syntax appear just like constructors and methods, even if we all know a method desugars to a functions that take a resource as it’s first parameter in the canonical abi. It’s nice to have a distinction in wit that can be used by code generators for creating idiomatic C++, Rust, JS etc methods. Even if we give methods a faithful wat/binary repr (like, e.g. flag types, which are a shorthand for a struct full of bools), the wat/binary form will necessarily have much worse syntax than the wit will, and we think having a syntax that doesn’t send you rubbing your temples reading the component model spec will help adoption.
Speaking as someone who has had to read and write a nontrivial amount of wat over the last 5 years, it’s lovely for small examples and it’s pretty challenging for large, “real world” programs.