Synnefo » snf-ganeti

{-# LANGUAGE TemplateHaskell, QuasiQuotes #-}

{-| TemplateHaskell helper for HTools.

As TemplateHaskell require that splices be defined in a separate

module, we combine all the TemplateHaskell functionality that HTools

needs in this module (except the one for unittests).

-}

{-

Copyright (C) 2011 Google Inc.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.

-}

module Ganeti.THH ( declareSADT

                  , makeJSONInstance

                  , genOpID

                  , genOpCode

                  , noDefault

                  ) where

import Control.Monad (liftM)

import Data.Char

import Data.List

import Language.Haskell.TH

import qualified Text.JSON as JSON

-- * Helper functions

-- | Ensure first letter is lowercase.

--

-- Used to convert type name to function prefix, e.g. in @data Aa ->

-- aaToString@.

ensureLower :: String -> String

ensureLower [] = []

ensureLower (x:xs) = toLower x:xs

-- | Helper for quoted expressions.

varNameE :: String -> Q Exp

varNameE = varE . mkName

-- | showJSON as an expression, for reuse.

showJSONE :: Q Exp

showJSONE = varNameE "showJSON"

-- | ToString function name.

toStrName :: String -> Name

toStrName = mkName . (++ "ToString") . ensureLower

-- | FromString function name.

fromStrName :: String -> Name

fromStrName = mkName . (++ "FromString") . ensureLower

-- | Converts a name to it's varE/litE representations.

--

reprE :: Either String Name -> Q Exp

reprE = either stringE varE

-- * Template code for simple string-equivalent ADTs

-- | Generates a data type declaration.

--

-- The type will have a fixed list of instances.

strADTDecl :: Name -> [String] -> Dec

strADTDecl name constructors =

    DataD [] name []

              (map (flip NormalC [] . mkName) constructors)

              [''Show, ''Read, ''Eq, ''Enum, ''Bounded, ''Ord]

-- | Generates a toString function.

--

-- This generates a simple function of the form:

--

-- @

-- nameToString :: Name -> String

-- nameToString Cons1 = var1

-- nameToString Cons2 = \"value2\"

-- @

genToString :: Name -> Name -> [(String, Either String Name)] -> Q [Dec]

genToString fname tname constructors = do

  sigt <- [t| $(conT tname) -> String |]

  -- the body clauses, matching on the constructor and returning the

  -- string value

  clauses <- mapM  (\(c, v) -> clause [recP (mkName c) []]

                             (normalB (reprE v)) []) constructors

  return [SigD fname sigt, FunD fname clauses]

-- | Generates a fromString function.

--

-- The function generated is monadic and can fail parsing the

-- string. It is of the form:

--

-- @

-- nameFromString :: (Monad m) => String -> m Name

-- nameFromString s | s == var1       = Cons1

--                  | s == \"value2\" = Cons2

--                  | otherwise = fail /.../

-- @

genFromString :: Name -> Name -> [(String, Name)] -> Q [Dec]

genFromString fname tname constructors = do

  -- signature of form (Monad m) => String -> m $name

  sigt <- [t| (Monad m) => String -> m $(conT tname) |]

  -- clauses for a guarded pattern

  let varp = mkName "s"

      varpe = varE varp

  clauses <- mapM (\(c, v) -> do

                     -- the clause match condition

                     g <- normalG [| $varpe == $(varE v) |]

                     -- the clause result

                     r <- [| return $(conE (mkName c)) |]

                     return (g, r)) constructors

  -- the otherwise clause (fallback)

  oth_clause <- do

    g <- normalG [| otherwise |]

    r <- [|fail ("Invalid string value for type " ++

                 $(litE (stringL (nameBase tname))) ++ ": " ++ $varpe) |]

    return (g, r)

  let fun = FunD fname [Clause [VarP varp]

                        (GuardedB (clauses++[oth_clause])) []]

  return [SigD fname sigt, fun]

-- | Generates a data type from a given string format.

--

-- The format is expected to multiline. The first line contains the

-- type name, and the rest of the lines must contain two words: the

-- constructor name and then the string representation of the

-- respective constructor.

--

-- The function will generate the data type declaration, and then two

-- functions:

--

-- * /name/ToString, which converts the type to a string

--

-- * /name/FromString, which (monadically) converts from a string to the type

--

-- Note that this is basically just a custom show/read instance,

-- nothing else.

declareSADT :: String -> [(String, Name)] -> Q [Dec]

declareSADT sname cons = do

  let name = mkName sname

      ddecl = strADTDecl name (map fst cons)

      -- process cons in the format expected by genToString

      cons' = map (\(a, b) -> (a, Right b)) cons

  tostr <- genToString (toStrName sname) name cons'

  fromstr <- genFromString (fromStrName sname) name cons

  return $ ddecl:tostr ++ fromstr

-- | Creates the showJSON member of a JSON instance declaration.

--

-- This will create what is the equivalent of:

--

-- @

-- showJSON = showJSON . /name/ToString

-- @

--

-- in an instance JSON /name/ declaration

genShowJSON :: String -> Q [Dec]

genShowJSON name = [d| showJSON = JSON.showJSON . $(varE (toStrName name)) |]

-- | Creates the readJSON member of a JSON instance declaration.

--

-- This will create what is the equivalent of:

--

-- @

-- readJSON s = case readJSON s of

--                Ok s' -> /name/FromString s'

--                Error e -> Error /description/

-- @

--

-- in an instance JSON /name/ declaration

genReadJSON :: String -> Q Dec

genReadJSON name = do

  let s = mkName "s"

  body <- [| case JSON.readJSON $(varE s) of

               JSON.Ok s' -> $(varE (fromStrName name)) s'

               JSON.Error e ->

                   JSON.Error $ "Can't parse string value for type " ++

                           $(stringE name) ++ ": " ++ e

           |]

  return $ FunD (mkName "readJSON") [Clause [VarP s] (NormalB body) []]

-- | Generates a JSON instance for a given type.

--

-- This assumes that the /name/ToString and /name/FromString functions

-- have been defined as by the 'declareSADT' function.

makeJSONInstance :: Name -> Q [Dec]

makeJSONInstance name = do

  let base = nameBase name

  showJ <- genShowJSON base

  readJ <- genReadJSON base

  return [InstanceD [] (AppT (ConT ''JSON.JSON) (ConT name)) (readJ:showJ)]

-- * Template code for opcodes

-- | Transforms a CamelCase string into an_underscore_based_one.

deCamelCase :: String -> String

deCamelCase =

    intercalate "_" . map (map toUpper) . groupBy (\_ b -> not $ isUpper b)

-- | Computes the name of a given constructor

constructorName :: Con -> Q Name

constructorName (NormalC name _) = return name

constructorName (RecC name _)    = return name

constructorName x                = fail $ "Unhandled constructor " ++ show x

-- | Builds the constructor-to-string function.

--

-- This generates a simple function of the following form:

--

-- @

-- fname (ConStructorOne {}) = "CON_STRUCTOR_ONE"

-- fname (ConStructorTwo {}) = "CON_STRUCTOR_TWO"

-- @

--

-- This builds a custom list of name/string pairs and then uses

-- 'genToString' to actually generate the function

genOpID :: Name -> String -> Q [Dec]

genOpID name fname = do

  TyConI (DataD _ _ _ cons _) <- reify name

  cnames <- mapM (liftM nameBase . constructorName) cons

  let svalues = map (Left . deCamelCase) cnames

  genToString (mkName fname) name $ zip cnames svalues

-- | OpCode parameter (field) type

type OpParam = (String, Q Type, Q Exp)

-- | Generates the OpCode data type.

--

-- This takes an opcode logical definition, and builds both the

-- datatype and the JSON serialisation out of it. We can't use a

-- generic serialisation since we need to be compatible with Ganeti's

-- own, so we have a few quirks to work around.

--

-- There are three things to be defined for each parameter:

--

-- * name

--

-- * type; if this is 'Maybe', will only be serialised if it's a

--   'Just' value

--

-- * default; if missing, won't raise an exception, but will instead

--   use the default

--

genOpCode :: String                -- ^ Type name to use

          -> [(String, [OpParam])] -- ^ Constructor name and parameters

          -> Q [Dec]

genOpCode name cons = do

  decl_d <- mapM (\(cname, fields) -> do

                    -- we only need the type of the field, without Q

                    fields' <- mapM (\(_, qt, _) ->

                                         qt >>= \t -> return (NotStrict, t))

                               fields

                    return $ NormalC (mkName cname) fields')

            cons

  let declD = DataD [] (mkName name) [] decl_d [''Show, ''Read, ''Eq]

  (savesig, savefn) <- genSaveOpCode cons

  (loadsig, loadfn) <- genLoadOpCode cons

  return [declD, loadsig, loadfn, savesig, savefn]

-- | Checks whether a given parameter is options

--

-- This requires that it's a 'Maybe'.

isOptional :: Type -> Bool

isOptional (AppT (ConT dt) _) | dt == ''Maybe = True

isOptional _ = False

-- | Generates the \"save\" expression for a single opcode parameter.

--

-- There is only one special handling mode: if the parameter is of

-- 'Maybe' type, then we only save it if it's a 'Just' value,

-- otherwise we skip it.

saveField :: Name    -- ^ The name of variable that contains the value

          -> OpParam -- ^ Parameter definition

          -> Q Exp

saveField fvar (fname, qt, _) = do

  t <- qt

  let fnexp = stringE fname

      fvare = varE fvar

  (if isOptional t

   then [| case $fvare of

             Just v' -> [( $fnexp, $showJSONE v')]

             Nothing -> []

         |]

   else [| [( $fnexp, $showJSONE $fvare )] |])

-- | Generates the \"save\" clause for an entire opcode constructor.

--

-- This matches the opcode with variables named the same as the

-- constructor fields (just so that the spliced in code looks nicer),

-- and passes those name plus the parameter definition to 'saveField'.

saveConstructor :: String    -- ^ The constructor name

                -> [OpParam] -- ^ The parameter definitions for this

                             -- constructor

                -> Q Clause  -- ^ Resulting clause

saveConstructor sname fields = do

  let cname = mkName sname

  let fnames = map (\(n, _, _) -> mkName n) fields

  let pat = conP cname (map varP fnames)

  let felems = map (uncurry saveField) (zip fnames fields)

      -- now build the OP_ID serialisation

      opid = [| [( $(stringE "OP_ID"),

                   $showJSONE $(stringE . deCamelCase $ sname) )] |]

      flist = listE (opid:felems)

      -- and finally convert all this to a json object

      flist' = [| $(varNameE "makeObj") (concat $flist) |]

  clause [pat] (normalB flist') []

-- | Generates the main save opcode function.

--

-- This builds a per-constructor match clause that contains the

-- respective constructor-serialisation code.

genSaveOpCode :: [(String, [OpParam])] -> Q (Dec, Dec)

genSaveOpCode opdefs = do

  cclauses <- mapM (uncurry saveConstructor) opdefs

  let fname = mkName "saveOpCode"

  sigt <- [t| $(conT (mkName "OpCode")) -> JSON.JSValue |]

  return $ (SigD fname sigt, FunD fname cclauses)

-- | Generates the \"load\" field for a single parameter.

--

-- There is custom handling, depending on how the parameter is

-- specified. For a 'Maybe' type parameter, we allow that it is not

-- present (via 'Utils.maybeFromObj'). Otherwise, if there is a

-- default value, we allow the parameter to be abset, and finally if

-- there is no default value, we require its presence.

loadField :: OpParam -> Q (Name, Stmt)

loadField (fname, qt, qdefa) = do

  let fvar = mkName fname

  t <- qt

  defa <- qdefa

  -- these are used in all patterns below

  let objvar = varNameE "o"

      objfield = stringE fname

  bexp <- if isOptional t

          then [| $((varNameE "maybeFromObj")) $objvar $objfield |]

          else case defa of

                 AppE (ConE dt) defval | dt == 'Just ->

                   -- but has a default value

                   [| $(varNameE "fromObjWithDefault")

                      $objvar $objfield $(return defval) |]

                 ConE dt | dt == 'Nothing ->

                     [| $(varNameE "fromObj") $objvar $objfield |]

                 s -> fail $ "Invalid default value " ++ show s ++

                      ", expecting either 'Nothing' or a 'Just defval'"

  return (fvar, BindS (VarP fvar) bexp)

loadConstructor :: String -> [OpParam] -> Q Exp

loadConstructor sname fields = do

  let name = mkName sname

  fbinds <- mapM loadField fields

  let (fnames, fstmts) = unzip fbinds

  let cval = foldl (\accu fn -> AppE accu (VarE fn)) (ConE name) fnames

      fstmts' = fstmts ++ [NoBindS (AppE (VarE 'return) cval)]

  return $ DoE fstmts'

genLoadOpCode :: [(String, [OpParam])] -> Q (Dec, Dec)

genLoadOpCode opdefs = do

  let fname = mkName "loadOpCode"

      arg1 = mkName "v"

      objname = mkName "o"

      opid = mkName "op_id"

  st1 <- bindS (varP objname) [| liftM JSON.fromJSObject

                                 (JSON.readJSON $(varE arg1)) |]

  st2 <- bindS (varP opid) [| $(varNameE "fromObj")

                              $(varE objname) $(stringE "OP_ID") |]

  -- the match results (per-constructor blocks)

  mexps <- mapM (uncurry loadConstructor) opdefs

  fails <- [| fail $ "Unknown opcode " ++ $(varE opid) |]

  let mpats = map (\(me, c) ->

                       let mp = LitP . StringL . deCamelCase . fst $ c

                       in Match mp (NormalB me) []

                  ) $ zip mexps opdefs

      defmatch = Match WildP (NormalB fails) []

      cst = NoBindS $ CaseE (VarE opid) $ mpats++[defmatch]

      body = DoE [st1, st2, cst]

  sigt <- [t| JSON.JSValue -> JSON.Result $(conT (mkName "OpCode")) |]

  return $ (SigD fname sigt, FunD fname [Clause [VarP arg1] (NormalB body) []])

-- | No default type.

noDefault :: Q Exp

noDefault = conE 'Nothing