Change for SIP-62: betterFors #99
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KacperFKorban
changed the title
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I suppose that the manager stays the same. ping @lihaoyi |
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I think this looks reasonable, bit i dont know enough about dotty internals to know what rhe consequences of this would |
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Ping @sjrd |
He-Pin
reviewed
Dec 23, 2024
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| This kind of effect loop is pretty commonly used in Scala FP programs and often ends in `yield ()`. | ||
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| The problem with the desugaring of this for-comprehensions is that it leaks memory because the result of `loop` has to be mapped over with `_ => ()`, which often does nothing. |
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Will it then be desugared to two foreachs? as the _ will never be used anyway.
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In this case, it should end up with just one flatMap. It will eliminate the last map call. This is also what bm4 would do in this situation.
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A proposal of a new approach for implementing change
3from SIP-62: betterFors.TLDR:
Don't drop the trailing
mapwhen desugaring. Instead, mark the lastApplynode with aTrailingForMapattachment and move the optimization to a later phase (after typing). This way, we can make sure that the resulting type of thefordoesn't change.