liblwt-ocaml-dev - 5.9.0-1+b2 main

Lwt is a library for cooperative threads implemented in a monadic style.
Unlike preemptive threads, cooperative threads do not use a scheduler to
distribute processor time between threads. Instead, each thread must
announce that it wants to let the others run.
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This package contains all the development stuff you need to use the
core Lwt OCaml library in your programs.