Command.elm

snippetFromTheCompiler = with errorAndIO
    let importedVars <- mapM (canonicalizeValues env) (Map.toList interfaces)

        allTypes = concat (ctors : importedVars)
        vars     = concatMap (fst . snd) allTypes
        header   = Map.map snd (Map.fromList allTypes)
        environ  = noneNoDocs . T.CLet [ T.Scheme vars [] (noneNoDocs T.CTrue) header ]

        fvar <- liftIO $ T.var T.Flexible
        c    <- TcExpr.constrain env (program moduleBody) (T.varN fvar)

    return (header, environ c)

Do.hs

snippetFromTheCompiler = do
    importedVars <- mapM (canonicalizeValues env) (Map.toList interfaces)

    let allTypes = concat (ctors : importedVars)
        vars     = concatMap (fst . snd) allTypes
        header   = Map.map snd (Map.fromList allTypes)
        environ  = noneNoDocs . T.CLet [ T.Scheme vars [] (noneNoDocs T.CTrue) header ]

    fvar <- liftIO $ T.var T.Flexible
    c    <- TcExpr.constrain env (program moduleBody) (T.varN fvar)
    return (header, environ c)