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|
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE OverloadedStrings #-}
{- |
Module : Text.Pandoc.Lua.Util
Copyright : © 2012–2020 John MacFarlane,
© 2017-2020 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
, defineHowTo
, throwTopMessageAsError'
, callWithTraceback
, dofileWithTraceback
) where
import Control.Monad (unless, when)
import Data.Text (Text)
import Foreign.Lua ( Lua, NumArgs, NumResults, Peekable, Pushable, StackIndex
, Status, ToHaskellFunction )
import qualified Foreign.Lua as Lua
import qualified Text.Pandoc.UTF8 as UTF8
-- | 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)
-- | 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.throwMessage "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.throwMessage (modifier (UTF8.toString msg))
-- | Mark the context of a Lua computation for better error reporting.
defineHowTo :: String -> Lua a -> Lua a
defineHowTo ctx op = Lua.errorConversion >>= \ec ->
Lua.addContextToException ec ("Could not " <> ctx <> ": ") op
-- | 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
|
