Hey By default, GHCi uses bytecode, which interacts badly with some optimizations according to the GHC manual. However, you can force GHCi to use object-code via `-fobject-code`. There are some small disadvantages, but at least it works. {-# language OverloadedStrings #-} {-# OPTIONS_GHC -fobject-code -O1 #-} import Data.String import Debug.Trace data Foo = Foo deriving Show instance IsString Foo where fromString "Foo" = trace "**fromString**" Foo main = let { f Foo = "Foo" :: Foo; g _ = "Foo" :: Foo } in print $ map (f . g) [0..1] ghci> main [**fromString** Foo,Foo] - Kai On 07.12.21 13:16, Johannes Waldmann wrote:
Dear Cafe,
with OverloadedStrings, the compiler inserts `fromString` applications at String literals. I was wondering - are these floated out?
{-# language OverloadedStrings #-}
import Data.String import Debug.Trace
data Foo = Foo deriving Show
instance IsString Foo where fromString "Foo" = trace "**fromString**" Foo
main = let { f Foo = "Foo" :: Foo; g _ = "Foo" :: Foo } in print $ map (f . g) [0..1]
With ghc -O1, I get
**fromString** [Foo,Foo]
That's good - not just floated out, but also interned (? - both "Foo" are really the same, just one call)
With ghc -00, and in ghci, I get
**fromString** **fromString** **fromString** **fromString** [Foo,Foo]
no floating here. Is there a way to get this floated in ghci?
The background of my question is that overloaded strings, and ghci, are heavily used in Tidal Cycles https://hackage.haskell.org/package/tidal
I guess it's mostly fine, because it's rare (in live coding performance) that application code contains function definitions.
- J.
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