Manual: anonymous function in pipeline needs parentheses #43661
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Consider:
```julia
d = (1:10
.|> x -> x^2
|> sum
)
```
This seems to compute a sum of squares.
But it does not. It outputs a vector of squares. (Because `|> sum` is parsed as being part of the anonymous function's body).
Parentheses are needed for the desired (expected?) behaviour:
```julia
d = (1:10
.|> (x -> x^2)
|> sum
)
```
This PR adds a small note and example to the "Function composition and piping" section of the manual to flag this.
As an aside, this confusion is even present in the [docstring](https://docs.julialang.org/en/v1/base/base/#Base.:|%3E) for `|>`:
> Applies a function to the preceding argument. This allows for easy function chaining.
> ```julia
[1:5;] |> x->x.^2 |> sum |> inv
```
This is parsed as
```julia
[1:5;] |> x-> (x.^2 |> sum |> inv)
```
but it feels like the author meant
```julia
[1:5;] |> (x-> x.^2) |> sum |> inv)
```.
aviatesk
approved these changes
Jan 5, 2022
LilithHafner
pushed a commit
to LilithHafner/julia
that referenced
this pull request
Feb 22, 2022
…3661) Consider: ```julia d = (1:10 .|> x -> x^2 |> sum ) ``` This seems to compute a sum of squares. But it does not. It outputs a vector of squares. (Because `|> sum` is parsed as being part of the anonymous function's body). Parentheses are needed for the desired (expected?) behaviour: ```julia d = (1:10 .|> (x -> x^2) |> sum ) ``` This PR adds a small note and example to the "Function composition and piping" section of the manual to flag this. As an aside, this confusion is even present in the [docstring](https://docs.julialang.org/en/v1/base/base/#Base.:|%3E) for `|>`: > Applies a function to the preceding argument. This allows for easy function chaining. > ```julia [1:5;] |> x->x.^2 |> sum |> inv ``` This is parsed as ```julia [1:5;] |> x-> (x.^2 |> sum |> inv) ``` but it feels like the author meant ```julia [1:5;] |> (x-> x.^2) |> sum |> inv) ```.
LilithHafner
pushed a commit
to LilithHafner/julia
that referenced
this pull request
Mar 8, 2022
…3661) Consider: ```julia d = (1:10 .|> x -> x^2 |> sum ) ``` This seems to compute a sum of squares. But it does not. It outputs a vector of squares. (Because `|> sum` is parsed as being part of the anonymous function's body). Parentheses are needed for the desired (expected?) behaviour: ```julia d = (1:10 .|> (x -> x^2) |> sum ) ``` This PR adds a small note and example to the "Function composition and piping" section of the manual to flag this. As an aside, this confusion is even present in the [docstring](https://docs.julialang.org/en/v1/base/base/#Base.:|%3E) for `|>`: > Applies a function to the preceding argument. This allows for easy function chaining. > ```julia [1:5;] |> x->x.^2 |> sum |> inv ``` This is parsed as ```julia [1:5;] |> x-> (x.^2 |> sum |> inv) ``` but it feels like the author meant ```julia [1:5;] |> (x-> x.^2) |> sum |> inv) ```.
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Consider:
This seems to compute a sum of squares.
But it does not. It outputs a vector of squares. (Because
|> sumis parsed as being part of the anonymous function's body).Parentheses are needed for the desired (expected?) behaviour:
This PR adds a small note and example to the "Function composition and piping" section of the manual to flag this.
The goal is to avoid befuddlement of users who expect the syntax of the first example to mean that of the second.
As an aside, this confusion is also present in the docstring for
|>:This is parsed as
but it feels like the author meant
.