Add some more JavaScript rewrite rules ⚡

[jmackie]

This was prompted by seeing that...

huh = (res) -> do {
    match res with
    | Ok(_) -> some_effect
    | Err(_) -> some_effect
};

Generates...

function huh(res) {
  return () => {
    return (
      res[0] === "Ok"
        ? some_effect
        : res[0] === "Err"
        ? some_effect
        : (() => {
            throw new Error("Pattern match error");
          })()
    )(/* NOTE: here we're calling `some_effect` */);
  };
}

So I thought it might be sensible to rewrite (condition ? true_value : false_value)() to condition ? true_value() : false_value() (see here). But then I realised that can only be legit if the base case (i.e. the throw) is of a similar type to the other values in the ternary, else you could end up generating something { throw new Error("...") }(). Only if you do that, you can end up deferring the pattern match error, which would be kinda weird (we're not doing laziness here).

So in the end, I didn't do any of the above, but there are a few things left over from that exploration that are worth having.

[codecov]

Codecov Report

Merging #52 (ef49282) into main (abcde1e) will increase coverage by 0.48%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
+ Coverage   78.97%   79.45%   +0.48%     
==========================================
  Files         113      113              
  Lines        7700     7755      +55     
==========================================
+ Hits         6081     6162      +81     
+ Misses       1619     1593      -26     

Impacted Files	Coverage Δ
crates/ditto-codegen-js/src/convert.rs	96.34% <ø> (+0.40%)	⬆️
crates/ditto-codegen-js/src/optimize/rewrites.rs	100.00% <100.00%> (ø)
...ditto-checker/src/module/value_declarations/mod.rs	99.60% <0.00%> (+0.39%)	⬆️
crates/ditto-codegen-js/src/optimize/mod.rs	95.11% <0.00%> (+0.65%)	⬆️
crates/ditto-codegen-js/src/render.rs	100.00% <0.00%> (+1.68%)	⬆️
crates/ditto-checker/src/typechecker/mod.rs	98.20% <0.00%> (+1.79%)	⬆️
crates/ditto-ast/src/expression.rs	85.18% <0.00%> (+1.85%)	⬆️
crates/ditto-checker/src/typechecker/pre_ast.rs	100.00% <0.00%> (+3.22%)	⬆️
...ates/ditto-checker/src/typechecker/substitution.rs	98.52% <0.00%> (+4.41%)	⬆️

---

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[jmackie]

Typo 🤦