# Interpolate array elements into \`Base.Cartesian.@nif\`

**URL:** <https://discourse.julialang.org/t/interpolate-array-elements-into-base-cartesian-nif/9992>\
**Category:** General Usage\
**Tags:** metaprogramming\
**Created:** [March 26, 2018, 1:04pm UTC](https://discourse.julialang.org/t/interpolate-array-elements-into-base-cartesian-nif/9992 "2018-03-26T13:04:51Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![chakravala](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chakravala/32/6832_2.png) [@chakravala](https://discourse.julialang.org/u/chakravala)\
**Post date:** [March 26, 2018, 1:04pm UTC](https://discourse.julialang.org/t/interpolate-array-elements-into-base-cartesian-nif/9992/1 "2018-03-26T13:04:51Z")

</div>

This is a continuation of my question in [Function that creates generated function using interpolation? - #10 by chakravala](https://discourse.julialang.org/t/function-that-creates-generated-function-using-interpolation/9951/10)

However, since the original question in that topic is now solved, I have restated my new question in a simplifed and easier to understand form:

My goal is to produce an if-then quote block based on the array elements of `lex`:

```nohighlight
julia> lex = [:(x^2),:(2x),2];

julia> macroexpand(quote
           Base.Cartesian.@nif($(length(lex)),
               i->(p == i-1),
               i->($(:(lex[i]))))
       end)
quote # REPL[224], line 2:
    if p == 0
        lex[1]
    else 
        if p == 1
            lex[2]
        else 
            lex[3]
        end
    end
end

```

However, the code I want to end up with should look like this:

```nohighlight
quote # REPL[224], line 2:
    if p == 0
        x^2
    else 
        if p == 1
            2x
        else 
            2
        end
    end
end

```

Is it possible to do this using `Base.Cartesian.@nif` or do I need to create my own function that generates the if-then block structure? The main problem is that it does not seem to be possible to reference both `i` and `lex` at the same time in the same scope.

Please let me know if someone knows or figures out how to do it! Regards,

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [March 26, 2018, 1:23pm UTC](https://discourse.julialang.org/t/interpolate-array-elements-into-base-cartesian-nif/9992/2 "2018-03-26T13:23:36Z")

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I don’t think the `nif` macro supports this. It does evaluation of some “pure” expressions (e.g. basic arithmetic) but it cannot know that you want to evaluate the `getindex` function calls at macro expansion time and not runtime.