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Where does the name of the `pure` function in the `Applicative` type class come from?
At this point in my learning journey, I simply accepted that this function is called pure
(both in Haskell and in PureScript), but it would have helped a lot if I had known the reasoning behind this name.
Both the Haskell reference and the PureScript docs use the word "lift",
^{Haskell} Lift a value into the Structure.
^{PureScript}
pure
can be seen as the function which lifts functions of zero arguments
but lift
is already in use (e.g., for monad transformers^{Haskell, Purescript}).
The PureScript reference for pure
also uses the word "wrap", but I understand now why the functor explanations along the lines of "wrap value in a box" can be misleading or miss the point entirely. For these reasons, I do like the name pure
as it has no "baggage" and I can focus on understanding the topic without preconceptions.
Books and tutorials using the word "context" helped me understand the more abstract constructs, so I sometimes wondered if using "embed" would make sense here, but then I let it go.
Anyway, I still research from time to time to figure out pure
's etymology, but did not get any closer yet.
1 answer
The following users marked this post as Works for me:
User | Comment | Date |
---|---|---|
toraritte | (no comment) | Jun 3, 2024 at 10:00 |
A direct answer to your question of where the name comes from is the paper that introduced Applicative functors, Applicative programming with effects (PDF). Quoting from there:
The idea is that
pure
embeds pure computations into the pure fragment of an effectful world[.]
I would say this is indeed the intuition many Haskell (and presumably PureScript) programmers have for it.
The intuition is that a type like F a
for a monad or applicative functor F
models a computation that may have effects. pure x
then models the "effectful computation" that happens to have no effects and returns x
, i.e. is pure in the sense of "pure functional programming". The "lifting" intuition should also be reasonably clear here. We're "lifting" "pure" computations into the world of effectful computations.
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