[erlang-questions] How to understanding recursive inside comprehension lists?

[I Gusti Ngurah Oka Prinarjaya]

Hi,

Now I read Joe's book titled Programming Erlang 2nd Edition. I practice
some functions such as for/3, quicksort/1, pythag/1, and perms/1, and
perms/1 is the function that hard to understand.

I understand comprehension lists, I fully understand for/3, I fully
understand quicksort/1, pythag/1. But it's really hard for me to understand
perms/1. Please teach me how to read and understand this perms/1 function.

perms([]) -> [[]];
perms(List) -> [ [H|T] || H <- List, T <- perms(List--[H]) ].

Output:
1> lib_misc:perms("123").
["123","132","213","231","312","321"]

Please enlightenment

Thank you
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