Lua: add function `pandoc.template.apply`

The new function applies a context, containing variable assignments, to
a template.

2 files changed, 69 insertions, 19 deletions

diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/Context.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/Context.hs
index 126f3a82d..dfaa1ff87 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/Context.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/Context.hs
@@ -1,3 +1,6 @@
+{-# LANGUAGE FlexibleInstances    #-}
+{-# LANGUAGE LambdaCase           #-}
+{-# LANGUAGE OverloadedStrings    #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {- |
    Module      : Text.Pandoc.Lua.Marshaling.Context
@@ -10,19 +13,50 @@
 
 Marshaling instance for doctemplates Context and its components.
 -}
-module Text.Pandoc.Lua.Marshal.Context () where
-
-import qualified HsLua as Lua
-import HsLua (Pushable)
-import Text.DocTemplates (Context(..), Val(..), TemplateTarget)
-import Text.DocLayout (render)
-
-instance (TemplateTarget a, Pushable a) => Pushable (Context a) where
-  push (Context m) = Lua.push m
-
-instance (TemplateTarget a, Pushable a) => Pushable (Val a) where
-  push NullVal = Lua.push ()
-  push (BoolVal b) = Lua.push b
-  push (MapVal ctx) = Lua.push ctx
-  push (ListVal xs) = Lua.push xs
-  push (SimpleVal d) = Lua.push $ render Nothing d
+module Text.Pandoc.Lua.Marshal.Context
+  ( peekContext
+  , pushContext
+  ) where
+
+import Control.Monad ((<$!>))
+import Data.Text (Text)
+import HsLua as Lua
+import HsLua.Module.DocLayout (peekDoc, pushDoc)
+import Text.DocTemplates (Context(..), Val(..))
+
+instance Pushable (Context Text) where
+  push = pushContext
+
+instance Pushable (Val Text) where
+  push = pushVal
+
+-- | Retrieves a template context from the Lua stack.
+peekContext :: LuaError e => Peeker e (Context Text)
+peekContext idx = Context <$!> peekMap peekText peekVal idx
+
+-- | Pushes a template context to the Lua stack.
+pushContext :: LuaError e => Pusher e (Context Text)
+pushContext = pushMap pushText pushVal . unContext
+
+pushVal :: LuaError e => Pusher e (Val Text)
+pushVal = \case
+  NullVal     -> Lua.pushnil
+  BoolVal b   -> Lua.pushBool b
+  MapVal ctx  -> pushContext ctx
+  ListVal xs  -> pushList pushVal xs
+  SimpleVal d -> pushDoc d
+
+peekVal :: LuaError e => Peeker e (Val Text)
+peekVal idx = liftLua (ltype idx) >>= \case
+  TypeNil      -> pure NullVal
+  TypeBoolean  -> BoolVal <$!> peekBool idx
+  TypeNumber   -> SimpleVal <$!> peekDoc idx
+  TypeString   -> SimpleVal <$!> peekDoc idx
+  TypeTable    -> do
+    len <- liftLua $ Lua.rawlen idx
+    if len <= 0
+      then MapVal <$!> peekContext idx
+      else ListVal <$!> peekList peekVal idx
+  TypeUserdata -> SimpleVal <$!> peekDoc idx
+  _ -> failPeek =<<
+       typeMismatchMessage "Doc, string, boolean, table, or nil" idx
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Template.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Template.hs
index 967fe31a8..be769e988 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Template.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Template.hs
@@ -12,11 +12,14 @@ module Text.Pandoc.Lua.Module.Template
   ) where
 
 import HsLua
+import HsLua.Module.DocLayout (pushDoc)
 import Text.Pandoc.Error (PandocError)
-import Text.Pandoc.Lua.Marshal.Template (pushTemplate)
+import Text.Pandoc.Lua.Marshal.Context (peekContext)
+import Text.Pandoc.Lua.Marshal.Template (peekTemplate, pushTemplate)
 import Text.Pandoc.Lua.PandocLua (PandocLua (unPandocLua), liftPandocLua)
 import Text.Pandoc.Templates
-  (compileTemplate, getDefaultTemplate, runWithPartials, runWithDefaultPartials)
+  ( compileTemplate, getDefaultTemplate, renderTemplate
+  , runWithPartials, runWithDefaultPartials )
 
 import qualified Data.Text as T
 
@@ -35,7 +38,20 @@ documentedModule = Module
 -- | Template module functions.
 functions :: [DocumentedFunction PandocError]
 functions =
-  [ defun "compile"
+  [ defun "apply"
+     ### liftPure2 renderTemplate
+     <#> parameter peekTemplate "pandoc Template" "template" "template to apply"
+     <#> parameter peekContext "table" "context" "variable values"
+     =#> functionResult pushDoc "Doc" "rendered template"
+     #? T.unlines
+     [ "Applies a context with variable assignments to a template,"
+     , "returning the rendered template. The `context` parameter must be a"
+     , "table with variable names as keys and [Doc], string, boolean, or"
+     , "table as values, where the table can be either be a list of the"
+     , "aforementioned types, or a nested context."
+     ]
+
+  , defun "compile"
      ### (\template mfilepath -> unPandocLua $
            case mfilepath of
              Just fp -> runWithPartials (compileTemplate fp template)