# What if the \`if\` filter from generator statements worked in for loops too?
**URL:** https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581
**Category:** Internals & Design
**Created:** [March 28, 2022, 1:58am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581 "2022-03-28T01:58:59Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@maxkapur](https://discourse.julialang.org/u/maxkapur)
#### Post date: [March 28, 2022, 1:58am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581/1 "2022-03-28T01:58:59Z")
Julia lets you append `if` to a list comprehension to filter it inline:
```julia
julia> [j for j in rand(1:100, 20) if iseven(j)]
7-element Vector{Int64}:
12
82
64
58
84
76
32
```
Sometimes you want to do something similar in a for loop. Here is one way:
```julia
julia> for j in rand(1:100, 20)
if iseven(j)
println(j)
end
end
42
38
50
82
76
22
18
60
86
48
```
Here is another:
```julia
julia> for j in (j for j in rand(1:100, 20) if iseven(j))
println(j)
end
66
24
88
68
94
28
90
40
20
28
```
Would there be any issues with implementing the following syntax for the same?
```julia
julia> for j in rand(1:100, 20) if iseven(j)
println(j)
end
ERROR: syntax: incomplete: "for" at REPL[24]:1 requires end
Stacktrace:
[1] top-level scope
@ none:1
```
(The purpose of my question is less of a feature request and more to gain understanding of how Julia parses these kinds of if/end blocks.)
---
### Author:  [@jd-foster](https://discourse.julialang.org/u/jd-foster)
#### Post date: [March 28, 2022, 3:55am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581/2 "2022-03-28T03:55:29Z")
Might be useful for reference:
[https://docs.julialang.org/en/v1/manual/arrays/#Generator-Expressions](https://docs.julialang.org/en/v1/manual/arrays/#Generator-Expressions)
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [March 28, 2022, 6:03am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581/3 "2022-03-28T06:03:46Z")
> [@maxkapur](#):
>
> Would there be any issues with implementing the following syntax for the same?
>
> ```julia
> julia> for j in rand(1:100, 20) if iseven(j)
> println(j)
> end
>
> ERROR: syntax: incomplete: "for" at REPL[24]:1 requires end
> Stacktrace:
> [1] top-level scope
> @ none:1
>
> ```
This is simply equivalent to
```julia
for j in rand(1:100, 20)
if iseven(j)
println(j)
end
```
so it complains about the missing `end` for the for-loop. So the syntax does already work, you just need an extra end. There’s no real way around this either since otherwise it would be ambiguous where which block ends.
---
### Author:  [@maxkapur](https://discourse.julialang.org/u/maxkapur)
#### Post date: [March 28, 2022, 6:31am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581/4 "2022-03-28T06:31:57Z")
So why isn’t `end` required in the generator expression `[j for j in 1:100 if iseven(j) end]`?
I mean, I know that the answer is “because it’s a generator expression and not an if block”, but if Julia can figure out that this is a generator expression and not an if block, then would it be dangerous to have a syntactical rule that says “if `if` appears on the same line as a for loop declaration, treat it like you would in a generator expression”?
(Again, I’m not trying to be snarky here, just trying to improve my understanding by getting a sense for what is or isn’t possible and why.)
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [March 28, 2022, 6:42am UTC](https://discourse.julialang.org/t/what-if-the-if-filter-from-generator-statements-worked-in-for-loops-too/78581/5 "2022-03-28T06:42:57Z")
The difference is that the generator expression is unambiguously delimited by the `]`. Yes, in theory we could make this dependent on whether there’s a newline or a space before the `if`, but I don’t think it’s worth the inconsistency compared to how blocks are nested everywhere else. Contrary to Python, we generally try to avoid syntactically significant whitespace.