How to create a non-standard string literal with parameters in Julia?

New to Julia
,
1

Can someone answer my question o Stack Overflow: How to create a non-standard string literal with parameters in Julia?

2

how would you feel about putting the parameters inside the string with a special delimiter? so instead of

R1"abc"
R234"abc"

You’d have, for example choosing delimiter :,

R"1$:abc"
R"234$:abc"
3

Thank you, @adienes, for instant help! But I’m looking for a way to do exactly that. If it’s not possible, I would accept as solution as well.

4

I’m not sure I’m qualified to say what is or is not “possible,” strictly speaking, but I do suspect what you are asking for is very difficult.

A string macro R"..." is essentially the same as @R_str("...") over a raw string. So what this would be is a way to programmatically generate definitions for

macro R1_str ... end
macro R2_str ... end
...
macro R234_str ... end

Which, as you can see, might end up being a lot of definitions. It would sort of be like defining

plus1(x) = ...
plus2(x) = ...
plus234(x) = ...

Instead of just plus(x,y)

5

Yes, you got it. I would like to generate multiple definitions. A guy answered me on SO suggesting me using flags. I believe that is fine but doen’t solve my problem. I have a suite of tests with random integers like:

R1"abc"
R34"abc
R244"abc"

and I would have to create all macro definitions one by one…

The sugestion was:

julia> macro R_str(p,flag)
           rotate(flag, p)
       end
@R_str (macro with 1 method)

julia> R"hello"3
"llohe"

julia> R"abc"1
"cab"

julia> R"abc"244
"cab"
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6

You can use metaprogramming for your tests, e.g.

for n in rand(1:200, 20)
    @eval @test @R_str("abc", $n) == rotate("abc", $n)
end

macro R_str(s, n); rotate(s, n); end really seems like the idiomatic Julia solution here.

(The main utility of making this a string macro is for when s and n are literals, so that the rotate(s, n) call happens at compile-time. Otherwise you might as well just call rotate(s, n) directly.)

7

@stevengj you mean If I use integers as flags, right?

8

Right, so R"abc"13 etcetera.

1 Like
9

I found a solution:

for n in 0:26
    @eval macro $(Symbol(:R, n, :_str))(s)
        rotate($n, s)
    end
end

I am sure that using flags is the best approach but this does exactly what I need.

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