Add `if` to for-loops like in comprehensions

Internals & Design
1

apologies if this has been discussed before, but i was surprised it didn’t work when i naively tried it:

julia> for i in 1:10 if i>3
       @info i
       end

ERROR: syntax: incomplete: "for" at REPL[1]:1 requires end
Stacktrace:
 [1] top-level scope at REPL[1]:0

strange because the if clause works in comprehensions:

julia> [i for i in 1:10 if i>3]
7-element Array{Int64,1}:
  4
  5
  6
  7
  8
  9
 10

has there been any discussion on making this possible? why wouldn’t we want them to work similarly?

2

One way you could do it is with a generator.

foreach( (i for i in 1:10 if i>3) ) do i
    @info i
end
3

Or just (well, mostly) pressing return.

for i in 1:10
    if i>3
        @info i
    end
end
2 Likes
4

You could probably put the logic inside the range like

for i in filter(x -> x > 3,1:10)
@info i
end

(I didn’t test this)

5

even more straight forward…

for i in 4:10
    @info i
end

? :grin:

6

This syntax already means something:

julia> for i in 1:6 if i > 4
           @info i
       end end
[ Info: 5
[ Info: 6

In other words, you just need to add a second end to close the if block. Changing this would be a breaking change to where these blocks end.

17 Likes