Hi, I wonder why the combination of for and if is allowed in comprehension like nbe = sum(count(iseven,rv) for rv ∈ rvv if isodd(length(rv));init=0) but has to be written in two separate control flows statement in loops: #separate for and if in the loop form nbe = 0 for rv ∈ rvv …

I think the main reason is that it introduces a parsing ambiguity that depends on whitespace. Your first example needs two end. Your second needs one. The sum doesn’t have this ambiguity because generators to not use end. You can achieve you intend with the somewhat horrific: julia> for a in (a f…

@LaurentPlagne , I am unsure if your question is why the language designers didn’t accommodate the syntax you are inquiring about or why you experience the issue when using the not supported for/if combination. In scenarios like yours - and when comprehension is not the best pick, I like to do somet…

I think @odow already sufficiently answered the question of “why”. But if you’re also looking for working alternatives, you could use Iterators.filter: using .Iterators nbe3 = 0 for rv in Iterators.filter(isodd ∘ length, rvv) nbe3 += count(iseven, rv) end In other situations you would have t…

thank you all for these detailed answers !

I’ll just point out that [image] LaurentPlagne: for rv ∈ rvv if isodd(length(rv)) nbe += count(iseven,rv) end end can be written as for rv ∈ rvv if isodd(length(rv)) nbe += count(iseven,rv) end end :wink:

Why `for/if` syntax is not allowed in loops

Internals & Design

rafael.guerra September 15, 2024, 4:59pm 6

Linking identical thread for further insights.

Topic		Replies	Views
For .... if ... syntax? Internals & Design loops , control-flow	10	2628	June 3, 2024
Add `if` to for-loops like in comprehensions Internals & Design	5	825	January 21, 2020
What if the `if` filter from generator statements worked in for loops too? Internals & Design	4	589	March 28, 2022
`for i = 1:M, j = 1:N` discrepancy (loop vs comprehension/generator) Internals & Design syntax , loops	26	4394	December 28, 2022
Documentation for comprehensions with if and/or w/o comma General Usage question	3	602	April 17, 2019

Why `for/if` syntax is not allowed in loops

Related topics