Re: How to load & parse an HI (interface) file?

I _think_ I've found what I need from https://github.com/ghc/ghc/blob/8843a39b3c941b1908a8d839f52bc323f3b45081/com... On Sun, Dec 3, 2017 at 7:41 AM, Saurabh Nanda wrote:

...

I would be cautious about using the ghc-api hi file interfaces; hi files turn out to interact with a lot of low-level parts in complex ways (even to the extent that they're a large part of why ghc can't parallelize builds itself and attempts to change that have mostly failed).

Are you cautioning against using the GHC API (as opposed to the --show-iface command line interface) or using HI files themselves?

-- Saurabh.

On Sun, Dec 3, 2017 at 2:04 AM, Brandon Allbery wrote:

...

I would be cautious about using the ghc-api hi file interfaces; hi files turn out to interact with a lot of low-level parts in complex ways (even to the extent that they're a large part of why ghc can't parallelize builds itself and attempts to change that have mostly failed).

But if you must do this, you *really* want to have https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler ready to hand --- and go through it first so you have some idea of how it works; much of it is links to the lower level details (often straight into the source).

On Sat, Dec 2, 2017 at 10:59 AM, Saurabh Nanda wrote:

...

(GHC newbie alert -- is this the right mailing list for these kind of questions?)

I"m writing some code to figure out all the instances of particular type-classes and after exploring a lot of options (hlint, haskell-src-exts, annotations, doctests, etc), I realized that the compiler had already figured it out and written it to disk for me!

More digging led me to https://www.stackage.org/haddo ck/lts-9.0/ghc-8.0.2/LoadIface.html#v:loadSrcInterface after which I got stuck. How does one call this function? Specifically:

* What is SDoc and how to construct a reasonable value for this argument? * IsBootInterface would mostly be False, right? * What does `Maybe FastString` represent and how does one construct it? * Finally how does one evaluate the resulting monadic action to get access to the underlying `ModIface`?

-- Saurabh.

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