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clarify wording on pure-functions overview to allow immutable hidden state, and add an example#3134
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epic-64 commentedDec 21, 2024 • edited
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edited
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there are still some typos, sorry, marking it as draft until they are fixed |
| Impure functions often do one or more of these things: | ||
| - Read from hidden state, i.e., they accessvariables anddata not explicitly passed into the function as input parameters | ||
| - Read from hiddenmutablestate, i.e., they accessnon-constantdata that was not explicitly passed into the function as input parameters |
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"non-constant" is not really a synonym for "mutable". I would suggest using the word "mutable" again even if it feels a bit repetitive; it's more important to be precise.
| {% endtabs %} | ||
| The next example is bit more tricky. Here,`i` is not passed as a parameter, but instead referenced directly from the outside. | ||
| This works in Scala because functions act as closures - they can capture the state around them. As long as that state is*immutable*, such a closure is still considered pure. |
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Not sure this is the best wording since we usually use "state" to talk about mutable state. Not all of the time. I would suggest "capture values from enclosing scopes".
| The first key point of this section is the definition of a pure function: | ||
| >A_pure function_ is a function that depends only on its declared inputs and its implementation to produce its output. | ||
| >A_pure function_ is a function that depends only on its declared inputs, captured constants, and its implementation to produce its output. |
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suggest "closed-over values" rather than "captured constants"
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Updates the "pure functions" overview athttps://docs.scala-lang.org/scala3/book/fp-pure-functions.html