Add json decoder examples #7133
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zth
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Oct 27, 2024
tests/tests/src/json_decoders.mjs
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| let match = json.id; | ||
| if (match === undefined) { | ||
| return; | ||
| } | ||
| if (match === null) { | ||
| return; | ||
| } | ||
| if (typeof match !== "string") { | ||
| return; | ||
| } |
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Here the bottom case should be enough, as it covers the 2 cases on top as well.
zth
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Oct 27, 2024
tests/tests/src/json_decoders.mjs
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| let match$1 = json.name; | ||
| if (match$1 === undefined) { | ||
| return; | ||
| } | ||
| if (match$1 === null) { | ||
| return; | ||
| } | ||
| if (typeof match$1 !== "string") { | ||
| return; | ||
| } |
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Same here, bottom case is enough.
zth
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Oct 27, 2024
tests/tests/src/json_decoders.mjs
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| let match$2 = json.age; | ||
| if (match$2 === undefined) { | ||
| return; | ||
| } | ||
| if (match$2 === null) { | ||
| return; | ||
| } | ||
| if (typeof match$2 !== "number") { | ||
| return; | ||
| } |
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And same here, bottom case is enough.
zth
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Oct 27, 2024
tests/tests/src/json_decoders.mjs
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| } | ||
| let email = json.email; | ||
| let tmp; | ||
| tmp = email !== undefined && !(email === null || typeof email !== "string") ? email : undefined; |
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This one is similar to the above - typeof email !== "string" ? undefined : email or even typeof email === "string" ? email : undefined would be ideal.
zth
commented
Oct 27, 2024
tests/tests/src/json_decoders.mjs
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| return; | ||
| } | ||
| let match$2 = json.users; | ||
| if (match$2 !== undefined && !(match$2 === null || !Array.isArray(match$2))) { |
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Same here - Array.isArray(match$2) would cover these.
|
Let's cut down and use the latest compiler: type group = {
id: string,
name: string,
}
let decodeGroup = group => {
switch group {
| (dict{"id": JSON.String(id), "name": String(name)}) =>
Some({
id,
name,
})
| _ => None
}
}gives: function decodeGroup(group) {
let match = group.id;
if (match === undefined) {
return;
}
if (match === null) {
return;
}
if (typeof match !== "string") {
return;
}
let match$1 = group.name;
if (match$1 !== undefined && !(match$1 === null || typeof match$1 !== "string")) {
return {
id: match,
name: match$1
};
}
} |
|
Looks like this is not about untagged variants: The same example with tagged variants has the same shape:
|
|
One might need special, different algorithms to compile untagged variants pattern matching differently. |
First step: remove the distinction between cases with and without payload in the toplevel algorithm. On this test: ```res @unboxed type rec t = | Boolean(bool) | @as(null) Null | String(string) | Number(float) | Object(Dict.t<t>) | Array(array<t>) type group = { id: string, name: string, } let decodeGroup = group => { switch group { | (dict{"id": String(id), "name": String(name)}) => (id, name) | _ => ("e", "f") } } ``` Before: ```js function decodeGroup(group) { let match = group.id; if (match === undefined) { return [ "e", "f" ]; } if (match === null) { return [ "e", "f" ]; } if (typeof match !== "string") { return [ "e", "f" ]; } let match$1 = group.name; if (match$1 !== undefined && !(match$1 === null || typeof match$1 !== "string")) { return [ match, match$1 ]; } else { return [ "e", "f" ]; } } ``` After: ``` function decodeGroup(group) { let match = group.id; if (match === undefined) { return [ "e", "f" ]; } if (typeof match !== "string") { return [ "e", "f" ]; } let match$1 = group.name; if (match$1 !== undefined && typeof match$1 === "string") { return [ match, match$1 ]; } else { return [ "e", "f" ]; } } ``` The 3 cases have become 2: check for optional fields and check for which case it is.
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More examples for when unboxed variant pattern matching code isn't as efficient as it could be.