Re: ghc command line arguments parsing

On 18 August 2016 at 20:51, Sven Panne wrote:

2016-08-17 16:37 GMT+02:00 Harendra Kumar :

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ghc accepts a flag and its argument as a single quoted or escaped argument as well. For example all of the following are equivalent:

ghc -package foo ghc "-package foo" ghc -package\ foo

Is this by design or accidental?

I would call this a bug, probably some missing quoting somewhere: Most commands I know don't do splitting on the arguments for themselves. Just try e.g.

gcc "-v -v"

Initially I too thought the same but then I did some more testing and it turned out that the way ghc does not really parse it exactly in the same way as independent unquoted arguments. It only parses a flag which takes an argument. For example: ghc "-package foo" -- parses foo as an argument to the -package flag ghc "-package foo -v" -- is not the same as "-package foo" and "-v" arguments passed independently, it is "foo -v" as the argument to "-package" So it essentially allows packing a flag and its argument together. Which provides a nice way to pass flags and their values as a single unit. This may be accidental to begin with but I liked this just because it makes passing opaque flags combined with arguments from a wrapper program like runghc much more convenient. I cannot think of any downside of this behavior unless someone points out otherwise.

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This has a nice side effect to make passing ghc arguments via rughc simple. For example runghc "-package foo" or runghc -package\ foo will pass "-package foo" to ghc. The alternative and documented way to achieve the same effect is runghc -package --ghc-arg=foo which is not that convenient.

My question is - can we rely on this way of parsing? If it is not by design, does it make sense to legalize and therefore document this?

And my question is: Can we fix this bug? :-D If this is not considered a bug, we should be very explicit about this deviation from standard behavior in the documentation, including the reasons for it.

As I explained above, I would prefer to keep this bug :-) and document it especially for runghc as a better alternative to --ghc-arg=foo . So instead of saying: runghc -package --ghc-arg=text -package --ghc-arg=turtle hello.hs We can just say: runghc "-package text" "-package turtle" hello.hs -harendra