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Laziness in Haskell — Part 3: Demand (www.youtube.com)

submitted 2 years ago by jaror@kbin.social to c/haskell@kbin.social

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To better understand some counterintuitive evaluation puzzles, we explore the notion of “demand” as it exists in Haskell and discuss how it influences GHC’s choice of evaluation strategy.

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[–] soltech@kbin.social 2 points 2 years ago

This video series is really great!

[–] jaror@kbin.social 2 points 2 years ago* (last edited 2 years ago)

I think pseq does have that "thunk forcing" behavior:

import GHC.Conc (pseq)

val :: Int
val = let x = error "x"
          y = error "y"
      in y `pseq` (x + y)

main = print val

I believe this is guaranteed to show the y error and not the x error.