Add defer statement - #377
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Add Go-style defer to the language: defer f(args) evaluates the function and its arguments at the defer statement and runs the call when the surrounding function returns, in LIFO order. Deferred calls also run when the function exits with an error, and at the top level they run when the script ends. An error raised by a deferred call becomes the function error unless the body already failed. The function return value is never changed by defers.
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Adds Go-style
deferto the language.defer f(args)evaluates the function and arguments at the defer statement and runs the call when the surrounding function returns, in LIFO order. Deferred calls also run when the function exits with an error, and top-level defers run when the script ends. The return value is never changed by defers; an error from a deferred call is reported only when the body did not already fail.Parser gets a DEFER token and four stmt rules mirroring
go. The VM captures calls in a per-invocationdefersslice onrunInfoStructand runs them after the body. No measurable overhead when defer is unused (geomean -0.5%, interleaved benchstat n=6).