Hi Tim,

Several years ago I wrote a proof of concept of one way to implement this in Haskell, http://johnlato.blogspot.com/2012/10/runtime-meta-programming-in-haskell.html.

I used TH to automatically lift expressions into a newtype-wrapped ExpQ that could be used for staged evaluation. More than one stage would probably have been tedious though, and a major problem with any non-trivial code was getting all the imports in place. I do think it would have been possible to automatically track imports though.

Of course that was 5 years ago, so state of the art has moved on. TH has better facilities for this now, and the ghc API probably has something better too.


On Fri, Nov 17, 2017, 10:06 Tim Sheard <sheard@pdx.edu> wrote:
After many years of hoping someone else would do this, I would like to
make GHC into a true multi-stage programming language. Here is how I
thought I might approach this.

1) Use the GHC as a library module.
2) Use the LLVM backend.

I have no experience with either of these tools.
Lets start simple, How would I write functions like

compile :: String -> IO PtrToLLVMCode  -- where the string is a small
Haskell program.
llvmCompile :: PtrToLLVMCode -> IO PtrToMachineCode
jumpTo:: PtrToMachineCode -> IO ans   -- where ans is the "type" of the
string.


Any thoughts on how to get started? What papers to read, examples to
look at?

I'd love to move to some more disciplined input type, a sort of (mono)
typed program
representation (with similar complexity) to Template Haskell Exp type.

where (Exp t) is a data structure representing a Haskell program of type t.

All offers of advice accepted. I'm trying to get started soon, and good
advice
about what to avoid is especially welcome.  If any one wanted to help
with this,
that would be great.

Tim Sheard

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