How to send a Lambda function from commandline to a Haskell program?

Question

What I would like to achieve:

./myHaskellProgram aLambdaFunc aFilePath

This aLambdaFunc is a string that the user provides and will run on the aFilePath.

I suppose I need Template Haskell and parse the aLambdaFunc string? Is there an easier way to do this?

Template haskell (and quasi quoters) runs at compile time, not at runtime. You will need to work with some parser that transforms it into a function. You can make use of the ghc parser source code to define such parser. — Willem Van Onsem, Aug 03 '21 at 18:59
@WillemVanOnsem Wow that's really a hidden gem on Hackage! Super cool, thx! — daydaynatation, Aug 03 '21 at 19:46

score 0 · Answer 1 · answered Aug 03 '21 at 23:24

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You could just load your program into ghci and let the user type Haskell expressions. And you can do a bit better using a custom quasi quoter.

answered Aug 03 '21 at 23:24

David Fox

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score 0 · Answer 2 · answered Aug 04 '21 at 09:24

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You could either use a system call to invoke GHCI (very unsafe) or you could write an entire parser.

You have an example on the ihaskell project, which uses a parser to create an interactive kernel compatible with Jupyter Notebook.

answered Aug 04 '21 at 09:24

David Davó

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score 0 · Answer 3 · answered Aug 04 '21 at 11:59

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The mueval package attempts to sandbox and execute Haskell code at runtime. It seems to be what you're looking for. It is(was) used in production by Chris Done's Try Haskell and some parts of lambdabot.

answered Aug 04 '21 at 11:59

Ari Fordsham

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How to send a Lambda function from commandline to a Haskell program?

3 Answers3