Actually all those loop types are supported in SNEX, if you take a look at the SNEX test suite, you'll see a bunch of test cases that use them:
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HISE/tools/snex_playground/test_files/loop/for_loop2.h at develop · christophhart/HISE
The open source framework for sample based instruments - HISE/tools/snex_playground/test_files/loop/for_loop2.h at develop · christophhart/HISE
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GitHub (github.com)
BTW, most features of the SNEX language are covered by a test file, so if you want to explore what is working, you can build the SNEX playground (tools/snex_playground), then click on the SNEX logo on the top left to load any test (there are about 500 tests in there). It's also a great way of reporting bugs within the SNEX language, so if you find anything, just write a test file that reproduces the issue and I'll add it to the list (that's how I implemented most of the SNEX language features).
However in most cases you don't need to write these manual loops and can just iterate every value of a container using the range based for loop. This is a known concept in C++ (and for(n in myArray) is the HiseScript equivalent.
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Range-Based For Loops in C++11 - Cprogramming.com
Learn how to easily loop over containers using the new C++11 range-based for loops--and how to add support for range-based for loops to your own classes!
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