(*  Title:      Tools/Code/code_haskell.ML

     Author:     Florian Haftmann, TU Muenchen

 Serializer for Haskell.

 *)

 signature CODE_HASKELL =

 sig

   val language_params: string

   val target: string

   val setup: theory -> theory

 end;

 structure Code_Haskell : CODE_HASKELL =

 struct

 val target = "Haskell";

 val language_extensions =

   ["EmptyDataDecls", "RankNTypes", "ScopedTypeVariables"];

 val language_pragma =

   "{-# LANGUAGE " ^ commas language_extensions ^ " #-}";

 val language_params =

   space_implode " " (map (prefix "-X") language_extensions);

 open Basic_Code_Thingol;

 open Code_Printer;

 infixr 5 @@;

 infixr 5 @|;

 (** Haskell serializer **)

 fun print_haskell_stmt class_syntax tyco_syntax const_syntax

     reserved deresolve deriving_show =

   let

     fun class_name class = case class_syntax class

      of NONE => deresolve class

       | SOME class => class;

     fun print_typcontext tyvars vs = case maps (fn (v, sort) => map (pair v) sort) vs

      of [] => []

       | constraints => enum "," "(" ")" (

           map (fn (v, class) =>

             str (class_name class ^ " " ^ lookup_var tyvars v)) constraints)

           @@ str " => ";

     fun print_typforall tyvars vs = case map fst vs

      of [] => []

       | vnames => str "forall " :: Pretty.breaks

           (map (str o lookup_var tyvars) vnames) @ str "." @@ Pretty.brk 1;

     fun print_tyco_expr tyvars fxy (tyco, tys) =

       brackify fxy (str tyco :: map (print_typ tyvars BR) tys)

     and print_typ tyvars fxy (tyco `%% tys) = (case tyco_syntax tyco

          of NONE => print_tyco_expr tyvars fxy (deresolve tyco, tys)

           | SOME (_, print) => print (print_typ tyvars) fxy tys)

       | print_typ tyvars fxy (ITyVar v) = (str o lookup_var tyvars) v;

     fun print_typdecl tyvars (tyco, vs) =

       print_tyco_expr tyvars NOBR (tyco, map ITyVar vs);

     fun print_typscheme tyvars (vs, ty) =

       Pretty.block (print_typforall tyvars vs @ print_typcontext tyvars vs @| print_typ tyvars NOBR ty);

     fun print_term tyvars some_thm vars fxy (IConst const) =

           print_app tyvars some_thm vars fxy (const, [])

       | print_term tyvars some_thm vars fxy (t as (t1 `$ t2)) =

           (case Code_Thingol.unfold_const_app t

            of SOME app => print_app tyvars some_thm vars fxy app

             | _ =>

                 brackify fxy [

                   print_term tyvars some_thm vars NOBR t1,

                   print_term tyvars some_thm vars BR t2

                 ])

       | print_term tyvars some_thm vars fxy (IVar NONE) =

           str "_"

       | print_term tyvars some_thm vars fxy (IVar (SOME v)) =

           (str o lookup_var vars) v

       | print_term tyvars some_thm vars fxy (t as _ `|=> _) =

           let

             val (binds, t') = Code_Thingol.unfold_pat_abs t;

             val (ps, vars') = fold_map (print_bind tyvars some_thm BR o fst) binds vars;

           in brackets (str "\\" :: ps @ str "->" @@ print_term tyvars some_thm vars' NOBR t') end

       | print_term tyvars some_thm vars fxy (ICase case_expr) =

           (case Code_Thingol.unfold_const_app (#primitive case_expr)

            of SOME (app as ({ name = c, ... }, _)) => if is_none (const_syntax c)

                 then print_case tyvars some_thm vars fxy case_expr

                 else print_app tyvars some_thm vars fxy app

             | NONE => print_case tyvars some_thm vars fxy case_expr)

     and print_app_expr tyvars some_thm vars ({ name = c, dom, range, annotate, ... }, ts) =

       let

         val ty = Library.foldr (fn (ty1, ty2) => Code_Thingol.fun_tyco `%% [ty1, ty2]) (dom, range)

         val printed_const =

           if annotate then

             brackets [(str o deresolve) c, str "::", print_typ tyvars NOBR ty]

           else

             (str o deresolve) c

       in 

         printed_const :: map (print_term tyvars some_thm vars BR) ts

       end

     and print_app tyvars = gen_print_app (print_app_expr tyvars) (print_term tyvars) const_syntax

     and print_bind tyvars some_thm fxy p = gen_print_bind (print_term tyvars) some_thm fxy p

     and print_case tyvars some_thm vars fxy { clauses = [], ... } =

           (brackify fxy o Pretty.breaks o map str) ["error", "\"empty case\""]

       | print_case tyvars some_thm vars fxy (case_expr as { clauses = [_], ... }) =

           let

             val (binds, body) = Code_Thingol.unfold_let (ICase case_expr);

             fun print_match ((pat, _), t) vars =

               vars

               |> print_bind tyvars some_thm BR pat

               |>> (fn p => semicolon [p, str "=", print_term tyvars some_thm vars NOBR t])

             val (ps, vars') = fold_map print_match binds vars;

           in brackify_block fxy (str "let {")

             ps

             (concat [str "}", str "in", print_term tyvars some_thm vars' NOBR body])

           end

       | print_case tyvars some_thm vars fxy { term = t, typ = ty, clauses = clauses as _ :: _, ... } =

           let

             fun print_select (pat, body) =

               let

                 val (p, vars') = print_bind tyvars some_thm NOBR pat vars;

               in semicolon [p, str "->", print_term tyvars some_thm vars' NOBR body] end;

           in Pretty.block_enclose

             (concat [str "(case", print_term tyvars some_thm vars NOBR t, str "of", str "{"], str "})")

             (map print_select clauses)

           end;

     fun print_stmt (name, Code_Thingol.Fun (_, (((vs, ty), raw_eqs), _))) =

           let

             val tyvars = intro_vars (map fst vs) reserved;

             fun print_err n =

               semicolon (

                 (str o deresolve) name

                 :: map str (replicate n "_")

                 @ str "="

                 :: str "error"

                 @@ (str o ML_Syntax.print_string

                     o Long_Name.base_name o Long_Name.qualifier) name

               );

             fun print_eqn ((ts, t), (some_thm, _)) =

               let

                 val consts = fold Code_Thingol.add_constnames (t :: ts) [];

                 val vars = reserved

                   |> intro_base_names

                       (is_none o const_syntax) deresolve consts

                   |> intro_vars ((fold o Code_Thingol.fold_varnames)

                       (insert (op =)) ts []);

               in

                 semicolon (

                   (str o deresolve) name

                   :: map (print_term tyvars some_thm vars BR) ts

                   @ str "="

                   @@ print_term tyvars some_thm vars NOBR t

                 )

               end;

           in

             Pretty.chunks (

               semicolon [

                 (str o suffix " ::" o deresolve) name,

                 print_typscheme tyvars (vs, ty)

               ]

               :: (case filter (snd o snd) raw_eqs

                of [] => [print_err ((length o fst o Code_Thingol.unfold_fun) ty)]

                 | eqs => map print_eqn eqs)

             )

           end

       | print_stmt (name, Code_Thingol.Datatype (_, (vs, []))) =

           let

             val tyvars = intro_vars vs reserved;

           in

             semicolon [

               str "data",

               print_typdecl tyvars (deresolve name, vs)

             ]

           end

       | print_stmt (name, Code_Thingol.Datatype (_, (vs, [((co, _), [ty])]))) =

           let

             val tyvars = intro_vars vs reserved;

           in

             semicolon (

               str "newtype"

               :: print_typdecl tyvars (deresolve name, vs)

               :: str "="

               :: (str o deresolve) co

               :: print_typ tyvars BR ty

               :: (if deriving_show name then [str "deriving (Read, Show)"] else [])

             )

           end

       | print_stmt (name, Code_Thingol.Datatype (_, (vs, co :: cos))) =

           let

             val tyvars = intro_vars vs reserved;

             fun print_co ((co, _), tys) =

               concat (

                 (str o deresolve) co

                 :: map (print_typ tyvars BR) tys

               )

           in

             semicolon (

               str "data"

               :: print_typdecl tyvars (deresolve name, vs)

               :: str "="

               :: print_co co

               :: map ((fn p => Pretty.block [str "| ", p]) o print_co) cos

               @ (if deriving_show name then [str "deriving (Read, Show)"] else [])

             )

           end

       | print_stmt (name, Code_Thingol.Class (_, (v, (super_classes, classparams)))) =

           let

             val tyvars = intro_vars [v] reserved;

             fun print_classparam (classparam, ty) =

               semicolon [

                 (str o deresolve) classparam,

                 str "::",

                 print_typ tyvars NOBR ty

               ]

           in

             Pretty.block_enclose (

               Pretty.block [

                 str "class ",

                 Pretty.block (print_typcontext tyvars [(v, map fst super_classes)]),

                 str (deresolve name ^ " " ^ lookup_var tyvars v),

                 str " where {"

               ],

               str "};"

             ) (map print_classparam classparams)

           end

       | print_stmt (_, Code_Thingol.Classinst { class, tyco, vs, inst_params, ... }) =

           let

             val tyvars = intro_vars (map fst vs) reserved;

             fun requires_args classparam = case const_syntax classparam

              of NONE => NONE

               | SOME (Code_Printer.Plain_const_syntax _) => SOME 0

               | SOME (Code_Printer.Complex_const_syntax (k,_ )) => SOME k;

             fun print_classparam_instance ((classparam, const), (thm, _)) =

               case requires_args classparam

                of NONE => semicolon [

                       (str o Long_Name.base_name o deresolve) classparam,

                       str "=",

                       print_app tyvars (SOME thm) reserved NOBR (const, [])

                     ]

                 | SOME k =>

                     let

                       val { name = c, dom, range, ... } = const;

                       val (vs, rhs) = (apfst o map) fst

                         (Code_Thingol.unfold_abs (Code_Thingol.eta_expand k (const, [])));

                       val s = if (is_some o const_syntax) c

                         then NONE else (SOME o Long_Name.base_name o deresolve) c;

                       val vars = reserved

                         |> intro_vars (map_filter I (s :: vs));

                       val lhs = IConst { name = classparam, typargs = [],

                         dicts = [], dom = dom, range = range, annotate = false } `$$ map IVar vs;

                         (*dictionaries are not relevant at this late stage,

                           and these consts never need type annotations for disambiguation *)

                     in

                       semicolon [

                         print_term tyvars (SOME thm) vars NOBR lhs,

                         str "=",

                         print_term tyvars (SOME thm) vars NOBR rhs

                       ]

                     end;

           in

             Pretty.block_enclose (

               Pretty.block [

                 str "instance ",

                 Pretty.block (print_typcontext tyvars vs),

                 str (class_name class ^ " "),

                 print_typ tyvars BR (tyco `%% map (ITyVar o fst) vs),

                 str " where {"

               ],

               str "};"

             ) (map print_classparam_instance inst_params)

           end;

   in print_stmt end;

 fun haskell_program_of_program labelled_name module_alias module_prefix reserved =

   let

     fun namify_fun upper base (nsp_fun, nsp_typ) =

       let

         val (base', nsp_fun') =

           Name.variant (if upper then first_upper base else base) nsp_fun;

       in (base', (nsp_fun', nsp_typ)) end;

     fun namify_typ base (nsp_fun, nsp_typ) =

       let

         val (base', nsp_typ') = Name.variant (first_upper base) nsp_typ;

       in (base', (nsp_fun, nsp_typ')) end;

     fun namify_stmt (Code_Thingol.Fun (_, (_, SOME _))) = pair

       | namify_stmt (Code_Thingol.Fun _) = namify_fun false

       | namify_stmt (Code_Thingol.Datatype _) = namify_typ

       | namify_stmt (Code_Thingol.Datatypecons _) = namify_fun true

       | namify_stmt (Code_Thingol.Class _) = namify_typ

       | namify_stmt (Code_Thingol.Classrel _) = pair

       | namify_stmt (Code_Thingol.Classparam _) = namify_fun false

       | namify_stmt (Code_Thingol.Classinst _) = pair;

     fun select_stmt (Code_Thingol.Fun (_, (_, SOME _))) = false

       | select_stmt (Code_Thingol.Fun _) = true

       | select_stmt (Code_Thingol.Datatype _) = true

       | select_stmt (Code_Thingol.Datatypecons _) = false

       | select_stmt (Code_Thingol.Class _) = true

       | select_stmt (Code_Thingol.Classrel _) = false

       | select_stmt (Code_Thingol.Classparam _) = false

       | select_stmt (Code_Thingol.Classinst _) = true;

   in

     Code_Namespace.flat_program labelled_name

       { module_alias = module_alias, module_prefix = module_prefix,

         reserved = reserved, empty_nsp = (reserved, reserved), namify_stmt = namify_stmt,

         modify_stmt = fn stmt => if select_stmt stmt then SOME stmt else NONE }

   end;

 fun serialize_haskell module_prefix string_classes { labelled_name, reserved_syms,

     includes, module_alias, class_syntax, tyco_syntax, const_syntax } program =

   let

     (* build program *)

     val reserved = fold (insert (op =) o fst) includes reserved_syms;

     val { deresolver, flat_program = haskell_program } = haskell_program_of_program

       labelled_name module_alias module_prefix (Name.make_context reserved) program;

     (* print statements *)

     fun deriving_show tyco =

       let

         fun deriv _ "fun" = false

           | deriv tycos tyco = not (tyco = Code_Thingol.fun_tyco)

               andalso (member (op =) tycos tyco

               orelse case try (Graph.get_node program) tyco

                 of SOME (Code_Thingol.Datatype (_, (_, cs))) => forall (deriv' (tyco :: tycos))

                     (maps snd cs)

                  | NONE => true)

         and deriv' tycos (tyco `%% tys) = deriv tycos tyco

               andalso forall (deriv' tycos) tys

           | deriv' _ (ITyVar _) = true

       in deriv [] tyco end;

     fun print_stmt deresolve = print_haskell_stmt

       class_syntax tyco_syntax const_syntax (make_vars reserved)

       deresolve (if string_classes then deriving_show else K false);

     (* print modules *)

     val import_includes_ps =

       map (fn (name, _) => str ("import qualified " ^ name ^ ";")) includes;

     fun print_module_frame module_name ps =

       (module_name, Pretty.chunks2 (

         str ("module " ^ module_name ^ " where {")

         :: ps

         @| str "}"

       ));

     fun print_module module_name (gr, imports) =

       let

         val deresolve = deresolver module_name

         fun print_import module_name = (semicolon o map str) ["import qualified", module_name];

         val import_ps = import_includes_ps @ map (print_import o fst) imports;

         fun print_stmt' gr name = case Graph.get_node gr name

          of (_, NONE) => NONE

           | (_, SOME stmt) => SOME (markup_stmt name (print_stmt deresolve (name, stmt)));

         val body_ps = map_filter (print_stmt' gr) ((flat o rev o Graph.strong_conn) gr);

       in

         print_module_frame module_name

           ((if null import_ps then [] else [Pretty.chunks import_ps]) @ body_ps)

       end;

     (*serialization*)

     fun write_module width (SOME destination) (module_name, content) =

           let

             val _ = File.check_dir destination;

             val filepath = (Path.append destination o Path.ext "hs" o Path.explode o implode

               o separate "/" o Long_Name.explode) module_name;

             val _ = Isabelle_System.mkdirs (Path.dir filepath);

           in

             (File.write filepath o format [] width o Pretty.chunks2)

               [str language_pragma, content]

           end

       | write_module width NONE (_, content) = writeln (format [] width content);

   in

     Code_Target.serialization

       (fn width => fn destination => K () o map (write_module width destination))

       (fn present => fn width => rpair (try (deresolver ""))

         o format present width o Pretty.chunks o map snd)

       (map (uncurry print_module_frame o apsnd single) includes

         @ map (fn module_name => print_module module_name (Graph.get_node haskell_program module_name))

           ((flat o rev o Graph.strong_conn) haskell_program))

   end;

 val serializer : Code_Target.serializer =

   Code_Target.parse_args (Scan.optional (Args.$$$ "root" -- Args.colon |-- Args.name) ""

     -- Scan.optional (Args.$$$ "string_classes" >> K true) false

     >> (fn (module_prefix, string_classes) =>

       serialize_haskell module_prefix string_classes));

 val literals = let

   fun char_haskell c =

     let

       val s = ML_Syntax.print_char c;

     in if s = "'" then "\\'" else s end;

   fun numeral_haskell k = if k >= 0 then string_of_int k

     else Library.enclose "(" ")" (signed_string_of_int k);

 in Literals {

   literal_char = Library.enclose "'" "'" o char_haskell,

   literal_string = quote o translate_string char_haskell,

   literal_numeral = numeral_haskell,

   literal_positive_numeral = numeral_haskell,

   literal_alternative_numeral = numeral_haskell,

   literal_naive_numeral = numeral_haskell,

   literal_list = enum "," "[" "]",

   infix_cons = (5, ":")

 } end;

 (** optional monad syntax **)

 fun pretty_haskell_monad c_bind =

   let

     fun dest_bind t1 t2 = case Code_Thingol.split_pat_abs t2

      of SOME ((pat, ty), t') =>

           SOME ((SOME ((pat, ty), true), t1), t')

       | NONE => NONE;

     fun dest_monad c_bind_name (IConst { name = c, ... } `$ t1 `$ t2) =

           if c = c_bind_name then dest_bind t1 t2

           else NONE

       | dest_monad _ t = case Code_Thingol.split_let t

          of SOME (((pat, ty), tbind), t') =>

               SOME ((SOME ((pat, ty), false), tbind), t')

           | NONE => NONE;

     fun implode_monad c_bind_name = Code_Thingol.unfoldr (dest_monad c_bind_name);

     fun print_monad print_bind print_term (NONE, t) vars =

           (semicolon [print_term vars NOBR t], vars)

       | print_monad print_bind print_term (SOME ((bind, _), true), t) vars = vars

           |> print_bind NOBR bind

           |>> (fn p => semicolon [p, str "<-", print_term vars NOBR t])

       | print_monad print_bind print_term (SOME ((bind, _), false), t) vars = vars

           |> print_bind NOBR bind

           |>> (fn p => semicolon [str "let", str "{", p, str "=", print_term vars NOBR t, str "}"]);

     fun pretty _ [c_bind'] print_term thm vars fxy [(t1, _), (t2, _)] = case dest_bind t1 t2

      of SOME (bind, t') => let

           val (binds, t'') = implode_monad c_bind' t'

           val (ps, vars') = fold_map (print_monad (gen_print_bind (K print_term) thm) print_term)

             (bind :: binds) vars;

         in

           (brackify fxy o single o enclose "do { " " }" o Pretty.breaks)

             (ps @| print_term vars' NOBR t'')

         end

       | NONE => brackify_infix (1, L) fxy

           (print_term vars (INFX (1, L)) t1, str ">>=", print_term vars (INFX (1, X)) t2)

   in (2, ([c_bind], pretty)) end;

 fun add_monad target' raw_c_bind thy =

   let

     val c_bind = Code.read_const thy raw_c_bind;

   in if target = target' then

     thy

     |> Code_Target.add_const_syntax target c_bind

         (SOME (Code_Printer.complex_const_syntax (pretty_haskell_monad c_bind)))

   else error "Only Haskell target allows for monad syntax" end;

 (** Isar setup **)

 val _ =

   Outer_Syntax.command @{command_spec "code_monad"} "define code syntax for monads"

     (Parse.term_group -- Parse.name >> (fn (raw_bind, target) =>

       Toplevel.theory  (add_monad target raw_bind)));

 val setup =

   Code_Target.add_target

     (target, { serializer = serializer, literals = literals,

       check = { env_var = "ISABELLE_GHC", make_destination = I,

         make_command = fn module_name =>

           "\"$ISABELLE_GHC\" " ^ language_params  ^ " -odir build -hidir build -stubdir build -e \"\" " ^

             module_name ^ ".hs" } })

   #> Code_Target.add_tyco_syntax target "fun" (SOME (2, fn print_typ => fn fxy => fn [ty1, ty2] =>

       brackify_infix (1, R) fxy (

         print_typ (INFX (1, X)) ty1,

         str "->",

         print_typ (INFX (1, R)) ty2

       )))

   #> fold (Code_Target.add_reserved target) [

       "hiding", "deriving", "where", "case", "of", "infix", "infixl", "infixr",

       "import", "default", "forall", "let", "in", "class", "qualified", "data",

       "newtype", "instance", "if", "then", "else", "type", "as", "do", "module"

     ]

   #> fold (Code_Target.add_reserved target) [

       "Prelude", "Main", "Bool", "Maybe", "Either", "Ordering", "Char", "String", "Int",

       "Integer", "Float", "Double", "Rational", "IO", "Eq", "Ord", "Enum", "Bounded",

       "Num", "Real", "Integral", "Fractional", "Floating", "RealFloat", "Monad", "Functor",

       "AlreadyExists", "ArithException", "ArrayException", "AssertionFailed", "AsyncException",

       "BlockedOnDeadMVar", "Deadlock", "Denormal", "DivideByZero", "DotNetException", "DynException",

       "Dynamic", "EOF", "EQ", "EmptyRec", "ErrorCall", "ExitException", "ExitFailure",

       "ExitSuccess", "False", "GT", "HeapOverflow",

       "IOError", "IOException", "IllegalOperation",

       "IndexOutOfBounds", "Just", "Key", "LT", "Left", "LossOfPrecision", "NoMethodError",

       "NoSuchThing", "NonTermination", "Nothing", "Obj", "OtherError", "Overflow",

       "PatternMatchFail", "PermissionDenied", "ProtocolError", "RecConError", "RecSelError",

       "RecUpdError", "ResourceBusy", "ResourceExhausted", "Right", "StackOverflow",

       "ThreadKilled", "True", "TyCon", "TypeRep", "UndefinedElement", "Underflow",

       "UnsupportedOperation", "UserError", "abs", "absReal", "acos", "acosh", "all",

       "and", "any", "appendFile", "asTypeOf", "asciiTab", "asin", "asinh", "atan",

       "atan2", "atanh", "basicIORun", "blockIO", "boundedEnumFrom", "boundedEnumFromThen",

       "boundedEnumFromThenTo", "boundedEnumFromTo", "boundedPred", "boundedSucc", "break",

       "catch", "catchException", "ceiling", "compare", "concat", "concatMap", "const",

       "cos", "cosh", "curry", "cycle", "decodeFloat", "denominator", "div", "divMod",

       "doubleToRatio", "doubleToRational", "drop", "dropWhile", "either", "elem",

       "emptyRec", "encodeFloat", "enumFrom", "enumFromThen", "enumFromThenTo",

       "enumFromTo", "error", "even", "exp", "exponent", "fail", "filter", "flip",

       "floatDigits", "floatProperFraction", "floatRadix", "floatRange", "floatToRational",

       "floor", "fmap", "foldl", "foldl'", "foldl1", "foldr", "foldr1", "fromDouble",

       "fromEnum", "fromEnum_0", "fromInt", "fromInteger", "fromIntegral", "fromObj",

       "fromRational", "fst", "gcd", "getChar", "getContents", "getLine", "head",

       "id", "inRange", "index", "init", "intToRatio", "interact", "ioError", "isAlpha",

       "isAlphaNum", "isDenormalized", "isDigit", "isHexDigit", "isIEEE", "isInfinite",

       "isLower", "isNaN", "isNegativeZero", "isOctDigit", "isSpace", "isUpper", "iterate", "iterate'",

       "last", "lcm", "length", "lex", "lexDigits", "lexLitChar", "lexmatch", "lines", "log",

       "logBase", "lookup", "loop", "map", "mapM", "mapM_", "max", "maxBound", "maximum",

       "maybe", "min", "minBound", "minimum", "mod", "negate", "nonnull", "not", "notElem",

       "null", "numerator", "numericEnumFrom", "numericEnumFromThen", "numericEnumFromThenTo",

       "numericEnumFromTo", "odd", "or", "otherwise", "pi", "pred", 

       "print", "product", "properFraction", "protectEsc", "putChar", "putStr", "putStrLn",

       "quot", "quotRem", "range", "rangeSize", "rationalToDouble", "rationalToFloat",

       "rationalToRealFloat", "read", "readDec", "readField", "readFieldName", "readFile",

       "readFloat", "readHex", "readIO", "readInt", "readList", "readLitChar", "readLn",

       "readOct", "readParen", "readSigned", "reads", "readsPrec", "realFloatToRational",

       "realToFrac", "recip", "reduce", "rem", "repeat", "replicate", "return", "reverse",

       "round", "scaleFloat", "scanl", "scanl1", "scanr", "scanr1", "seq", "sequence",

       "sequence_", "show", "showChar", "showException", "showField", "showList",

       "showLitChar", "showParen", "showString", "shows", "showsPrec", "significand",

       "signum", "signumReal", "sin", "sinh", "snd", "span", "splitAt", "sqrt", "subtract",

       "succ", "sum", "tail", "take", "takeWhile", "takeWhile1", "tan", "tanh", "threadToIOResult",

       "throw", "toEnum", "toInt", "toInteger", "toObj", "toRational", "truncate", "uncurry",

       "undefined", "unlines", "unsafeCoerce", "unsafeIndex", "unsafeRangeSize", "until", "unwords",

       "unzip", "unzip3", "userError", "words", "writeFile", "zip", "zip3", "zipWith", "zipWith3"

     ] (*due to weird handling of ':', we can't do anything else than to import *all* prelude symbols*);

 end; (*struct*)