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Use Bool.true and Bool.false in FAQ

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Richard Feldman 2022-10-02 18:46:04 -04:00
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@ -95,20 +95,20 @@ the function might give different answers.
Both of these would make revising code riskier across the entire language, which is very undesirable.
Another option would be to define that function equality always returns `False`. So both of these would evaluate
to `False`:
Another option would be to define that function equality always returns `false`. So both of these would evaluate
to `false`:
- `(\x -> x + 1) == (\x -> 1 + x)`
- `(\x -> x + 1) == (\x -> x + 1)`
This makes function equality effectively useless, while still technically allowing it. It has some other downsides:
- Now if you put a function inside a record, using `==` on that record will still type-check, but it will then return `False`. This could lead to bugs if you didn't realize you had accidentally put a function in there - for example, because you were actually storing a different type (e.g. an opaque type) and didn't realize it had a function inside it.
- Now if you put a function inside a record, using `==` on that record will still type-check, but it will then return `false`. This could lead to bugs if you didn't realize you had accidentally put a function in there - for example, because you were actually storing a different type (e.g. an opaque type) and didn't realize it had a function inside it.
- If you put a function (or a value containing a function) into a `Dict` or `Set`, you'll never be able to get it out again. This is a common problem with [NaN](https://en.wikipedia.org/wiki/NaN), which is also defined not to be equal to itself.
The first of these problems could be addressed by having function equality always return `True` instead of `False` (since that way it would not affect other fields' equality checks in a record), but that design has its own problems:
The first of these problems could be addressed by having function equality always return true instead of false (since that way it would not affect other fields' equality checks in a record), but that design has its own problems:
- Although function equality is still useless, `(\x -> x + 1) == (\x -> x)` returns `True`. Even if it didn't lead to bugs in practice, this would certainly be surprising and confusing to beginners.
- Although function equality is still useless, `(\x -> x + 1) == (\x -> x)` returns `Bool.true`. Even if it didn't lead to bugs in practice, this would certainly be surprising and confusing to beginners.
- Now if you put several different functions into a `Dict` or `Set`, only one of them will be kept; the others will be discarded or overwritten. This could cause bugs if a value stored a function internally, and then other functions relied on that internal function for correctness.
Each of these designs makes Roc a language that's some combination of more error-prone, more confusing, and more