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Simon Marlow authored
Shortcut when switching evaluators: instead of going round the normal scheduler loop, just cut to the chase and run the thread using the other evaluator. This avoids doing stack squeezing each time we switch evaluators, which is an O(n) operation these days, whereas it used to be O(n) the first time, and O(1) thereafter if the stack hadn't changed too much. This is a problem that we should perhaps address separately, but for now the workaround should provide a speed boost to GHCi on the HEAD.
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