coc-settings.json

{
"languageserver": {
  "haskell": {
    "command": "haskell-language-server-wrapper",
    "args": ["--lsp"],
    "rootPatterns": [
      "*.cabal",
      "stack.yaml",
      "cabal.project",
      "package.yaml",
      "hie.yaml"
    ],
    "filetypes": [
      "haskell",
      "lhaskell"
    ],
    "initializationOptions": {
      "languageServerHaskell": {
      }
    }
  }
}
}