{- | Module : Text.DocTemplates Copyright : Copyright (C) 2009-2019 John MacFarlane License : BSD3 Maintainer : John MacFarlane <jgm@berkeley.edu> Stability : alpha Portability : portable The text templating system used by pandoc. == Example of use > {-# LANGUAGE OverloadedStrings #-} > import Data.Text (Text) > import qualified Data.Text.IO as T > import Data.Aeson > import Text.DocTemplates > > data Employee = Employee { firstName :: String > , lastName :: String > , salary :: Maybe Int } > instance ToJSON Employee where > toJSON e = object [ "name" .= object [ "first" .= firstName e > , "last" .= lastName e ] > , "salary" .= salary e ] > > template :: Text > template = "$for(employee)$Hi, $employee.name.first$. $if(employee.salary)$You make $employee.salary$.$else$No salary data.$endif$$sep$\n$endfor$" > > main :: IO () > main = do > res <- compileTemplate "mytemplate.txt" template > case res of > Left e -> error e > Right t -> T.putStrLn $ renderTemplate t $ object > ["employee" .= > [ Employee "John" "Doe" Nothing > , Employee "Omar" "Smith" (Just 30000) > , Employee "Sara" "Chen" (Just 60000) ] > ] == Delimiters To mark variables and control structures in the template, either @$@…@$@ or @${@…@}@ may be used as delimiters. The styles may also be mixed in the same template, but the opening and closing delimiter must match in each case. The opening delimiter may be followed by one or more spaces or tabs, which will be ignored. The closing delimiter may be followed by one or more spaces or tabs, which will be ignored. To include a literal @$@ in the document, use @$$@. == Comments Anything between the sequence @$--@ and the end of the line will be treated as a comment and omitted from the output. == Interpolated variables A slot for an interpolated variable is a variable name surrounded by matched delimiters. Variable names must begin with a letter and can contain letters, numbers, @_@, @-@, and @.@. The keywords @it@, @if@, @else@, @endif@, @for@, @sep@, and @endfor@ may not be used as variable names. Examples: > $foo$ > $foo.bar.baz$ > $foo_bar.baz-bim$ > $ foo $ > ${foo} > ${foo.bar.baz} > ${foo_bar.baz-bim} > ${ foo } The values of variables are determined by a JSON object that is passed as a parameter to @renderTemplate@. So, for example, @title@ will return the value of the @title@ field, and @employee.salary@ will return the value of the @salary@ field of the object that is the value of the @employee@ field. - If the value of the variable is a JSON string, the string will be rendered verbatim. (Note that no escaping is done on the string; the assumption is that the calling program will escape the strings appropriately for the output format.) - If the value is a JSON array, the values will be concatenated. - If the value is a JSON object, the string @true@ will be rendered. - If the value is a JSON number, it will be rendered as an integer if possible, otherwise as a floating-point number. - If the value is a JSON boolean, it will be rendered as @true@ if true, and as the empty string if false. - Every other value will be rendered as the empty string. The value of a variable that occurs by itself on a line will be indented to the same level as the opening delimiter of the variable. == Conditionals A conditional begins with @if(variable)@ (enclosed in matched delimiters) and ends with @endif@ (enclosed in matched delimiters). It may optionally contain an @else@ (enclosed in matched delimiters). The @if@ section is used if @variable@ has a non-empty value, otherwise the @else@ section is used (if present). (Note that even the string @false@ counts as a true value.) Examples: > $if(foo)$bar$endif$ > > $if(foo)$ > $foo$ > $endif$ > > $if(foo)$ > part one > $else$ > part two > $endif$ > > ${if(foo)}bar${endif} > > ${if(foo)} > ${foo} > ${endif} > > ${if(foo)} > ${ foo.bar } > ${else} > no foo! > ${endif} Conditional keywords should not be indented, or unexpected spacing problems may occur. == For loops A for loop begins with @for(variable)@ (enclosed in matched delimiters) and ends with @endfor@ (enclosed in matched delimiters. If @variable@ is an array, the material inside the loop will be evaluated repeatedly, with @variable@ being set to each value of the array in turn. If the value of the associated variable is not an array, a single iteration will be performed on its value. Examples: > $for(foo)$$foo$$sep$, $endfor$ > > $for(foo)$ > - $foo.last$, $foo.first$ > $endfor$ > > ${ for(foo.bar) } > - ${ foo.bar.last }, ${ foo.bar.first } > ${ endfor } You may optionally specify a separator between consecutive values using @sep@ (enclosed in matched delimiters). The material between @sep@ and the @endfor@ is the separator. > ${ for(foo) }${ foo }${ sep }, ${ endfor } Instead of using @variable@ inside the loop, the special anaphoric keyword @it@ may be used. > ${ for(foo.bar) } > - ${ it.last }, ${ it.first } > ${ endfor } == Partials Partials (subtemplates stored in different files) may be included using the syntax > ${ boilerplate() } The partials are obtained using @getPartial@ from the @TemplateMonad@ class. This may be implemented differently in different monads. The path passed to @getPartial@ is computed on the basis of the original template path (a parameter to @compileTemplate@) and the partial’s name. The partial’s name is substituted for the /base name/ of the original template path (leaving the original template’s extension), unless the partial has an explicit extension, in which case this is kept. So, with the @TemplateMonad@ instance for IO, partials will be sought in the directory containing the main template, and will be assumed to have the extension of the main template. Partials may optionally be applied to variables using a colon: > ${ date:fancy() } > > ${ articles:bibentry() } If @articles@ is an array, this will iterate over its values, applying the partial @bibentry()@ to each one. So the second example above is equivalent to > ${ for(articles) } > ${ it:bibentry() } > ${ endfor } Note that the anaphoric keyword @it@ must be used when iterating over partials. In the above examples, the @bibentry@ partial should contain @it.title@ (and so on) instead of @articles.title@. Final newlines are omitted from included partials. Partials may include other partials. If you exceed a nesting level of 50, though, in resolving partials, the literal @(loop)@ will be returned, to avoid infinite loops. A separator between values of an array may be specified in square brackets, immediately after the variable name or partial: > ${months[, ]}$ > > ${articles:bibentry()[; ]$ The separator in this case is literal and (unlike with @sep@ in an explicit @for@ loop) cannot contain interpolated variables or other template directives. -} module Text.DocTemplates ( renderTemplate , compileTemplate , compileTemplateFile , applyTemplate , TemplateMonad(..) , TemplateTarget(..) , Context(..) , Val(..) , ToContext(..) , FromContext(..) , Template -- export opaque type ) where import qualified Data.Text.IO as TIO import Data.Text (Text) import Text.DocTemplates.Parser (compileTemplate) import Text.DocTemplates.Internal ( TemplateMonad(..), Context(..), Val(..), ToContext(..), FromContext(..), TemplateTarget(..), Template, renderTemplate ) -- | Compile a template from a file. IO errors will be -- raised as exceptions; template parsing errors result in -- Left return values. compileTemplateFile :: FilePath -> IO (Either String Template) compileTemplateFile templPath = do templateText <- TIO.readFile templPath compileTemplate templPath templateText -- | Compile a template and apply it to a context. This is -- just a convenience function composing 'compileTemplate' -- and 'renderTemplate'. If a template will be rendered -- more than once in the same process, compile it separately -- for better performance. applyTemplate :: (TemplateMonad m, TemplateTarget a, ToContext a b) => FilePath -> Text -> b -> m (Either String a) applyTemplate fp t val = do res <- compileTemplate fp t case res of Left s -> return $ Left s Right t' -> return $ Right $ renderTemplate t' val