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flohofwoe • today at 4:19 PM • 1 reply • view on HN

Real-world WAT (WASM text format) looks more like this (e.g. it looks like a 'structured assembly' type of thing):

    i32.const 27512
    i32.load
    local.tee $var1
    if
      i32.const 27404
      i32.load
      local.get $var1
      call_indirect (param i32)
    end
S-expressions are only used outside such instruction blocks for the 'program-structure' (e.g. see: https://developer.mozilla.org/en-US/docs/WebAssembly/Referen...). IIRC early pre-release-versions of WASM were entirely built from S-expressions and as a 'pure stack machine' (I may remember wrong though).

To see what a complete WASM blob looks like in WAT format you can go here: https://floooh.github.io/sokol-html5/clear-sapp.html, open the browser devtools, go to the 'Sources' tab and click the `clear-sapp.wasm` file).

Replies

tlively • today at 4:57 PM

This is partially true, but the standard text format also allows the instructions to be nested as S-expressions, for example:

  (i32.add
    (i32.const 0)
    (i32.const 1))
Many projects, including the official spec test suite and the Binaryen test suite, primarily use this format.

> IIRC early pre-release-versions of WASM were entirely built from S-expressions and as a 'pure stack machine' (I may remember wrong though).

Yes, the S-expressions predate WebAssembly even being a stack machine. Originally the design was that it encoded an AST, so the folded S-expression format was the only option.

There was a lot of discussion back in the day (before my time) about creating a better text format, but no one could agree on what it should be, so they just defaulted to the S-expression idea and focused on getting WebAssembly out the door.