Ok. any suggestions how to get close to the C preprocessor behaviour though?
On Monday, 24 October 2016 11:13:18 UTC+2, Mauro wrote:
>
> On Mon, 2016-10-24 at 10:37, Florian Oswald <florian...@gmail.com
> <javascript:>> wrote:
> > I have something that this in C++ I would write like
> >
> > double f(double x){
> > // do something with x
> > #ifdef MACROVAR
> > // do something else with x
> > #endif
> > return(x)
> > }
> >
> > I was trying to understand how i could use julia macro's to achieve
> > something similar. I have seen how the Logging.jl uses macros to this
> end,
> > at least that's how I understand
> > it:
> https://github.com/kmsquire/Logging.jl/blob/master/src/logging_macros.jl
> > . However I'm a bit unclear as to how to use this in my case. in my
> case,
> > the condition of whether or not to insert a piece of code is stored in a
> > custom type. Here is what I tried:
> >
> > # simplified type:
> > type Param
> > nD_rent :: Int
> > end
> >
> > # macro:
> > macro add_buy(p::Param)
> > quote
> > if $(esc(p.nD_rent)) > 4
> > # insert some additional code
> > println("here comes additional code")
> > println(typeof(p))
> >
> > else
> > println(typeof(p))
> > :nothing
> > end
> > end
> > end
>
> No, a macro receives the AST. Check this
>
> macro tmp(p)
> println(p)
> println(typeof(p))
> end
>
> So your signature should probably just read:
>
> macro add_buy(p)
> ...
> end
>
> > *julia> **bk.@add_buy(p)*
> >
> > *ERROR: MethodError: no method matching @add_buy(::Symbol)*
> >
> > Closest candidates are:
> >
> > @add_buy(*::bk.Param*) at
> > /Users/florian.oswald/git/bk/bk.jl/src/solver.jl:641
> >
> >
> > so, I have a type `Param`, and depending on the value in field nD_rent,
> I
> > would like to insert that code or not. thanks for any suggestions.
>
> That is not what your above macro does. And that is not what macros
> should do (ideally), they should be syntax transformations independent
> of the values. You can eval in a macro but that is *strongly*
> discouraged.
>
