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doc: primops: add more info for foldl (#9254)

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* doc: primops: add more info for foldl

From the existing doc it is not obvious whether the first or the
second argument is the accumulator. This is however relevant to
know, as for certain scenarios, this might change the behavior.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
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Philipp Schuster 2023-11-23 22:02:20 +01:00 committed by GitHub
parent bf13943206
commit 2ce8c9650b
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1 changed files with 10 additions and 3 deletions
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13
src/libexpr/primops.cc
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@ -3179,9 +3179,16 @@ static RegisterPrimOp primop_foldlStrict({
.doc = R"(
Reduce a list by applying a binary operator, from left to right,
e.g. `foldl' op nul [x0 x1 x2 ...] = op (op (op nul x0) x1) x2)
...`. For example, `foldl' (x: y: x + y) 0 [1 2 3]` evaluates to 6.
The return value of each application of `op` is evaluated immediately,
even for intermediate values.
...`.
For example, `foldl' (acc: elem: acc + elem) 0 [1 2 3]` evaluates
to `6` and `foldl' (acc: elem: { "${elem}" = elem; } // acc) {}
["a" "b"]` evaluates to `{ a = "a"; b = "b"; }`.
The first argument of `op` is the accumulator wheres the second
argument is the current element being processed. The return value
of each application of `op` is evaluated immediately, even for
intermediate values.
)",
.fun = prim_foldlStrict,
});