[mauro3]

Whilst Julia's foreign function interface is indeed good and it is really easy to call into C, the point is that Julia itself is as fast as C. So you don't need to write any C code to get performance, instead just tune the bottlenecks in Julia itself.

For instance, the standard library of Julia [1] is written in Julia itself (and is very performant) and only calls into external C or Fortran libraries where there are well established code-bases (e.g. BLAS, FFTW). Compare this to, e.g., Python or R where much of the standard library is written in C.

[1] https://github.com/JuliaLang/julia/tree/master/base