Reverse polish compiler in F# using LLVM, derived from this 35-line Racket example http://beautifulracket.com/stacker/source-listing.html

ReversePolishCompiler2.fs

let (|Int|_|) s =
  let mutable x = 0
  if System.Int32.TryParse(s, &x) then Some x else None

LLVM.NativeLibrary.LLVMDLL.Load()
LLVM.Target.InitializeNative()

let context = LLVM.Context.Global
let i32 = LLVM.IntegerType.GetInt32 context

let compile lines : System.Func<int> =
  let mdl = LLVM.Module("main", context)
  let ee = LLVM.ExecutionEngine mdl
  let fnType = LLVM.FunctionType i32
  let fn = mdl.CreateFunction("calc", fnType)
  let blk = LLVM.Block("blk", context, fn)
  let gen = LLVM.InstructionBuilder(context, blk)
  let constant x = i32.Constant(uint64 x, true) :> LLVM.Value
  let rec (|Parse|) = function
    | Int x::t -> constant x, t
    | "+"::Parse(x, Parse(y, t)) -> gen.Add(x, y), t
    | "*"::Parse(x, Parse(y, t)) -> gen.Multiply(x, y), t
  let (Parse(f, _)) = lines
  ignore(gen.Return f)
  let interop = LLVM.Interop.ClrInterop ee
  interop.GetDelegate(fn, mdl)

let lines = stdin.ReadToEnd().Split '\n' |> List.ofSeq |> List.rev
printfn "%d" ((compile lines).Invoke())