The LLVM LHC Haskell Optimization System
Haskell C LLVM
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Build Status

About LHC

The LHC Haskell Compiler aims at compiling Haskell2010 to LLVM IR using the HaskellSuite of libraries.

Getting started

LHC is built by stack:

stack setup
stack build
stack exec lhc

Installing the lhc-prim library is required before the example programs can be compiled.

stack install cabal-install
stack exec -- cabal update
cd packages/lhc-prim/
stack exec -- cabal install --haskell-suite -w `stack exec -- which lhc`

After lhc-prim has been installed, all the programs in examples/ will be compilable:

stack exec -- lhc build examples/HelloWorld.hs
lli examples/HelloWorld.ll

You can run lhc with the --keep-intermediate-files flag to inspect the various stages of the transformation from bedrock to llvm.

stack exec -- lhc build --verbose --keep-intermediate-files examples/HelloWorld.hs


Running the test suite is done via stack:

stack test && cat .stack-work/logs/lhc-*-test.log

Status (updated 2018-05-26)

LHC is comprised of separate libraries which are developed independenly and are in various states of completion.


Haskell-scope implements name resolution for a sizable subset of Haskell2010 but it's far from complete. So far it hasn't proved a bottleneck.


Haskell-tc implements type-checking and type-inference for a small subset of Haskell2010. Only the constructs used in the example programs are supported.


Haskell-crux is responsible for desugaring and, like haskell-tc, has only been defined for exactly those language constructs which are currently used by the example programs.

base library

The base is extremely minimal and functions are implemented on a by-need basis.

Integer support

None. Will eventually write a minimal implementation in either Haskell or C.


Not implemented yet but the RTS has been designed with exceptions in mind.

Garbage collection

LHC has a simple but accurate semispace garbage collector.


Not supported. Will eventually use libuv.

Unicode support

Not supported. Will eventually use libicu.

Compilation pipeline and the relevant libraries:

│     Parsing      │
│ haskell-src-exts │
│ Name resolution │
│  haskell-scope  │
 │ Type-checking │
 │  haskell-tc   │
  │  Desugaring  │
  │ haskell-crux │
│ Optimizing Core │
│       LHC       │
    │ Bedrock │
    │ bedrock │
 │ Generate LLVM │
 │    bedrock    │