Hi, I am new to Julia coming from Python. In Python we have the “partial” function that allow to derive a function by fixing some arguments. Can we do something similar in Julia? I would like to do something like: function f(x, y, z) x + y + z end and then create a function g(x) = f(x, y=compu…

How about this? f(x, y, z) = x + y + z computed_y() = (println("y_comp"); 2) computed_z() = (println("z_comp"); 3) g = let y, z y = computed_y() z = computed_z() g(x) = f(x, y, z) end g(1) == 6 Maybe a little bit awkward.

I think this is much better: f(x, y, z) = x + y + z computed_y() = (println("y_comp"); 2) computed_z() = (println("z_comp"); 3) @eval g(x) = f(x, $(computed_y()), $(computed_z())) g(1) == 6

You should not need eval for this. A closure is fine, eg f(x, y, z) = x + y + z y, z = 2, 3 g = x -> f(x, y, z) g(1)

The reason is… @tog seems to want one liner, plus he seems to like to know how to interpolate computed_y() stuff into the arguments once and for all, not every time of invocation. Practically, you are right. :slight_smile:

[image] Sijun: interpolate computed_y() stuff into the arguments once and for all, not every time of invocation I am not sure I understand what is meant here.

When we define g(x) in this way: g(x) = f(x, computed_y(), computed_z()) Everytime we call g(x), computed_y() and computed_z() will have to be calculated. What if we seek for an expression that looks very much like g(x) = f(x, computed_y(), computed_z()) but that takes the values of computed_x() …

You definitely don’t need and should not use eval for this, a simple closure will do. Eg let y, z = computed_y(), computed_z() x -> f(x, y, z) end or similar.

I agree eval should be used with care since its evaluation goes into global scope. Definitely the kind of expression I suggested should be discouraged.

@Sijun and @Tamas_Papp I think you have understood what I want to do i.e not recompute y & z each time the one argument instance is called. I am not sure I understand what you meant by global scope. I am not sure it is a good idea to make visible to new variables y & z as proposed initially by @Ta…

Can a function returns a partial function?

New to Julia

xiaodai December 18, 2019, 1:04am 3

See this discussion Is there a package to that can make partial functions automatically?

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Can a function returns a partial function?

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