Why cabal repl can play faster than cabal run

[WendaoLee]

Or for a short: What things that cabal run need to do but cabal repl not to do?Why these things cost so much time?

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I'm writing a Haskell programmer with cabal now.At the beginning,I always wrote some test cases in the main and used cabal run to check for it.But it always took about half-to-one minute on linking.Then I found cabal repl can play the same role,and I surprisingly found that cabal repl plays so faster than cabal run.According to the log in the terminal,it seems that cabal repl don't need link,it just compile and then go running.

That made me confused:Why cabal repl don't need Link?And what's the more that cabal run do?

I'm sorry it looks like a stupid question.But I'm really wonder the reason behind it.It smells so interesting. I'd appriciate if someone can give me any answer or reference.

[ulysses4ever]

For the same reason GHCi is faster to load a file than GHC to compile it: GHC's native backend is slow, but GHCi doesn't use the backend, it compiles to high-level bytecode (which it can interpret later on) rather than a native executable.

[Mikolaj]

No, another one. The .hi files are interface files. I think ghci doesn't write any files with the bytecode, which is yet another speedup. However, consult GHC documentation to make sure.

[fgaz]

@WendaoLee if you want to learn more about the general concepts, here are the respective wikipedia pages:

• https://en.wikipedia.org/wiki/Compiled_language
• https://en.wikipedia.org/wiki/Interpreter_(computing)

Haskell is both :)

[WendaoLee]

Ah, thanks. 😽 Though to be honest, I know these concepts(but I forgot GHCI interepted the program,thanks for your remind), and I was hoping someone might provide me with articles or references that delve deeper into the mechanisms behind these things when I asked this question... Well, I apologize if my expectations seemed a bit demanding and vexatious. I truly appreciate your help.

[ulysses4ever]

@WendaoLee it's all right. The thing is, you asked essentially a GHC question on a Cabal forum. You may have a better luck asking it on a GHC forum. For example, in the ghc-devs mailing list.

[WendaoLee]

Yes,you are right.😽Sorry for interruption.Thanks for your suggestion.