Asynchronously executes the body, returning immediately to the calling thread. Additionally, any visible calls to <!, >! and alt!/alts! channel operations within the body will block (if necessary) by 'parking' the calling thread rather than tying up an OS thread (or the only JS thread when in ClojureScript). Upon completion of the operation, the body will be resumed. go blocks should not (either directly or indirectly) perform operations that may block indefinitely. Doing so risks depleting the fixed pool of go block threads, causing all go block processing to stop. This includes core.async blocking ops (those ending in !!) and other blocking IO. Returns a channel which will receive the result of the body when completed