I think your code should not compile at all in its current form, as result = ch[0] is an incompatible assignment, string to float.
Generally parallel processing is restricted in Nim currently with default GC, as each thread has its own heap ans so passing data is difficult. I never used parallel in the last years, so I can not really help. But see post below, so problem seems to be known, and things will improve soon with new --gc:arc > [https://forum.nim-lang.org/t/1202](https://forum.nim-lang.org/t/1202)
