Add Delay type and use it #5910
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Fixes #5908. Unsure where to put this, it could go in its own module I guess.
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| -- | Force the evaluation of the expression delayed by the 'Delay'. | ||
| force :: Delay a -> a | ||
| force (Delay a) = a @BI.BuiltinUnit |
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I guess the BuiltinUnit is necessary in order for it to be compiled into delay and force?
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Mysteriously it compiles without it, but I think it's better to be explicit about doing the type instantiation.
plutus-tx/src/PlutusTx/Utils.hs
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| import Prelude as Haskell | ||
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| mustBeReplaced :: String -> a | ||
| mustBeReplaced placeholder = | ||
| error $ | ||
| "The " <> show placeholder <> " placeholder must have been replaced by the \ | ||
| \core-to-plc plugin during compilation." | ||
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| -- | Delay evalaution of the expression inside the 'Delay' constructor. | ||
| newtype Delay a = Delay (forall b. a) |
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@michaelpj what is the purpose of forall b here? I'd appreciate a comment.
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Huh, some tests fail. How surprising! |
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The problem with this is that the Haskell code you write using it is not delayed when used off-chain (and remember that we are using I'm not entirely sure how to fix this. If we actually want something that behaves differently on- and off-chain, then we probably need to bake it into the compiler. |
This is how its done in Purescript https://pursuit.purescript.org/packages/purescript-control/6.0.0/docs/Control.Lazy#v:defer : a thunk is involved at construction time. |
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Yes, but that's the unit-lambda approach which is what we were trying to avoid here. That said, I think this would still be a handy library tool even if all it does is wrap up that pattern. |
This is exactly how I was thinking about it. Same tool but more explicitly tagged. |
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Fixes #5908.
Unsure where to put this, it could go in its own module I guess.