aboutsummaryrefslogtreecommitdiff
path: root/src/Text/Pandoc/Lua/Util.hs
blob: 9c5da1088ae6fd49d2e7cec00ce4bc694d7571e5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{- |
   Module      : Text.Pandoc.Lua.Util
   Copyright   : © 2012–2019 John MacFarlane,
                 © 2017-2019 Albert Krewinkel
   License     : GNU GPL, version 2 or above

   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
   Stability   : alpha

Lua utility functions.
-}
module Text.Pandoc.Lua.Util
  ( getTag
  , rawField
  , addField
  , addFunction
  , addValue
  , pushViaConstructor
  , loadScriptFromDataDir
  , defineHowTo
  , throwTopMessageAsError'
  , callWithTraceback
  , dofileWithTraceback
  ) where

import Prelude
import Control.Monad (unless, when)
import Foreign.Lua ( Lua, NumArgs, NumResults, Peekable, Pushable, StackIndex
                   , Status, ToHaskellFunction )
import Text.Pandoc.Class (readDataFile, runIOorExplode, setUserDataDir)
import qualified Foreign.Lua as Lua
import qualified Text.Pandoc.UTF8 as UTF8
import Data.Text (Text)

-- | Get value behind key from table at given index.
rawField :: Peekable a => StackIndex -> String -> Lua a
rawField idx key = do
  absidx <- Lua.absindex idx
  Lua.push key
  Lua.rawget absidx
  Lua.popValue

-- | Add a value to the table at the top of the stack at a string-index.
addField :: Pushable a => String -> a -> Lua ()
addField = addValue

-- | Add a key-value pair to the table at the top of the stack.
addValue :: (Pushable a, Pushable b) => a -> b -> Lua ()
addValue key value = do
  Lua.push key
  Lua.push value
  Lua.rawset (Lua.nthFromTop 3)

-- | Add a function to the table at the top of the stack, using the given name.
addFunction :: ToHaskellFunction a => String -> a -> Lua ()
addFunction name fn = do
  Lua.push name
  Lua.pushHaskellFunction fn
  Lua.rawset (-3)

-- | Helper class for pushing a single value to the stack via a lua function.
-- See @pushViaCall@.
class PushViaCall a where
  pushViaCall' :: String -> Lua () -> NumArgs -> a

instance PushViaCall (Lua ()) where
  pushViaCall' fn pushArgs num = do
    Lua.push fn
    Lua.rawget Lua.registryindex
    pushArgs
    Lua.call num 1

instance (Pushable a, PushViaCall b) => PushViaCall (a -> b) where
  pushViaCall' fn pushArgs num x =
    pushViaCall' fn (pushArgs *> Lua.push x) (num + 1)

-- | Push an value to the stack via a lua function. The lua function is called
-- with all arguments that are passed to this function and is expected to return
-- a single value.
pushViaCall :: PushViaCall a => String -> a
pushViaCall fn = pushViaCall' fn (return ()) 0

-- | Call a pandoc element constructor within lua, passing all given arguments.
pushViaConstructor :: PushViaCall a => String -> a
pushViaConstructor pandocFn = pushViaCall ("pandoc." ++ pandocFn)

-- | Load a file from pandoc's data directory.
loadScriptFromDataDir :: Maybe FilePath -> FilePath -> Lua ()
loadScriptFromDataDir datadir scriptFile = do
  script <- Lua.liftIO . runIOorExplode $
            setUserDataDir datadir >> readDataFile scriptFile
  status <- Lua.dostring script
  when (status /= Lua.OK) $
    throwTopMessageAsError' (("Couldn't load '" ++ scriptFile ++ "'.\n") ++)

-- | Get the tag of a value. This is an optimized and specialized version of
-- @Lua.getfield idx "tag"@. It only checks for the field on the table at index
-- @idx@ and on its metatable, also ignoring any @__index@ value on the
-- metatable.
getTag :: StackIndex -> Lua String
getTag idx = do
  -- push metatable or just the table
  Lua.getmetatable idx >>= \hasMT -> unless hasMT (Lua.pushvalue idx)
  Lua.push ("tag" :: Text)
  Lua.rawget (Lua.nthFromTop 2)
  Lua.tostring Lua.stackTop <* Lua.pop 2 >>= \case
    Nothing -> Lua.throwException "untagged value"
    Just x -> return (UTF8.toString x)

-- | Modify the message at the top of the stack before throwing it as an
-- Exception.
throwTopMessageAsError' :: (String -> String) -> Lua a
throwTopMessageAsError' modifier = do
  msg <- Lua.tostring' Lua.stackTop
  Lua.pop 2 -- remove error and error string pushed by tostring'
  Lua.throwException (modifier (UTF8.toString msg))

-- | Mark the context of a Lua computation for better error reporting.
defineHowTo :: String -> Lua a -> Lua a
defineHowTo ctx = Lua.withExceptionMessage (("Could not " <> ctx <> ": ") <>)

-- | Like @'Lua.pcall'@, but uses a predefined error handler which adds a
-- traceback on error.
pcallWithTraceback :: NumArgs -> NumResults -> Lua Status
pcallWithTraceback nargs nresults = do
  let traceback' :: Lua NumResults
      traceback' = do
        l <- Lua.state
        msg <- Lua.tostring' (Lua.nthFromBottom 1)
        Lua.traceback l (Just (UTF8.toString msg)) 2
        return 1
  tracebackIdx <- Lua.absindex (Lua.nthFromTop (Lua.fromNumArgs nargs + 1))
  Lua.pushHaskellFunction traceback'
  Lua.insert tracebackIdx
  result <- Lua.pcall nargs nresults (Just tracebackIdx)
  Lua.remove tracebackIdx
  return result

-- | Like @'Lua.call'@, but adds a traceback to the error message (if any).
callWithTraceback :: NumArgs -> NumResults -> Lua ()
callWithTraceback nargs nresults = do
  result <- pcallWithTraceback nargs nresults
  when (result /= Lua.OK) Lua.throwTopMessage

-- | Run the given string as a Lua program, while also adding a traceback to the
-- error message if an error occurs.
dofileWithTraceback :: FilePath -> Lua Status
dofileWithTraceback fp = do
  loadRes <- Lua.loadfile fp
  case loadRes of
    Lua.OK -> pcallWithTraceback 0 Lua.multret
    _ -> return loadRes