Empty Basic Blocks

[nwtgck]

Hi, developers of llvm-hs-quote.

Environment

llvm-hs-quote: 1497273
stack solver: lts-10.3 (this is the same as llvm-hs-quote)

Proposal

Allow library users to use $bbs with empty [BasicBlock].

My concern

module11 [bBlock] has no error in the following code. However, module11 [] has a runtime error.

module11 :: [AST.Global.BasicBlock] -> AST.Module
module11 basicBlocks = [Quote.LLVM.llmod|
  define void @myfunc(i32 %a, i32 %b) {
    $bbs:basicBlocks
    ret void
  }
|]

runtime error message

Pattern match failure in do expression at ...

To avoid the empty-list problem, I should write the following. In the code, betterModule11 [] has no error, but it is redundant.

betterModule11 :: [AST.Global.BasicBlock] -> AST.Module
betterModule11 basicBlocks =
  if Prelude.null basicBlocks
    then
      [Quote.LLVM.llmod|
        define void @myfunc(i32 %a, i32 %b) {
          ret void
        }
      |]
    else
      [Quote.LLVM.llmod|
        define void @myfunc(i32 %a, i32 %b) {
          $bbs:basicBlocks
          ret void
        }
      |]

The code is just an example. In actual program using this library, allowing empty list is more convenient. I was wondering whether you allow to us use $bbs with empty [BasicBlock].