Question

This is a bit long, so bear with me!

I’m having a bit of trouble working with a Haskell program, that I have to use as part of a uni project. For reference, it’s Casper.

So, you’re supposed to execute a script, which is actually a Bash script to invoke Hugs interpreter like this:

exec $HUGSBIN/hugs $HUGSARGS +p"Casper> " $FILES

Where $FILES points to a Main.lhs file.

After this, I need to invoke a function “compile” with a path to a file, in the interpreter.

I need to perform the above in a scripted manner. I need this automated because I’m writing a program that will call on Casper in the background.

So I compiled the .lhs file. Now I want to execute the “compile” function but I have no idea how this is done. I try:

./Main compile <a path>

from the command line but it returns me an error about a file “test” not found. Upon investigation, I see these lines in the Main.lhs file:

>main :: String -> IO()
>main = compile "test"

>compile :: String -> IO()
>compile s = catch (compile0 False s) handler

[...snipped]

The 2nd line solves this question. Now my question is, how do I invoke the “compile” function and pass a path to it after I have compiled main.lhs? From the interpreter, I just type “compile ” and it works, but I can’t get the same to work after compiling the main.lhs and executing from the command line? Any ideas why? Is there any way I can script Hugs if all else fails?

Thank you for any assistance!

Answer 1

You may access the command-line arguments passed to a Haskell program via getArgs. For example, it sounds like you want a main function that does something like this:

>main = do
>    args <- getArgs
>    case args of
>        [] -> putStrLn "What file did you want me to compile?"
>        [filename] -> compile filename
>        _ -> putStrLn "I only compile one file at a time."

Modify to taste.