| Copyright | Copyright (C) 2009-2019 John MacFarlane |
|---|---|
| License | BSD3 |
| Maintainer | John MacFarlane <jgm@berkeley.edu> |
| Stability | alpha |
| Portability | portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Text.DocTemplates
Description
The text templating system used by pandoc.
Example of use
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
truewill 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
trueif 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.
Synopsis
- renderTemplate :: (TemplateTarget a, ToContext b a) => Template -> b -> a
- compileTemplate :: TemplateMonad m => FilePath -> Text -> m (Either String Template)
- compileTemplateFile :: FilePath -> IO (Either String Template)
- applyTemplate :: (TemplateMonad m, TemplateTarget a, ToContext b a) => FilePath -> Text -> b -> m (Either String a)
- class Monad m => TemplateMonad m where
- getPartial :: FilePath -> m Text
- class Monoid a => TemplateTarget a where
- newtype Context a = Context {}
- data Val a
- class ToContext b a where
- class FromContext a b where
- data Template
Documentation
renderTemplate :: (TemplateTarget a, ToContext b a) => Template -> b -> a Source #
Render a compiled template in a "context" which provides values for the template's variables.
compileTemplate :: TemplateMonad m => FilePath -> Text -> m (Either String Template) Source #
Compile a template. The FilePath parameter is used to determine a default path and extension for partials and may be left empty if partials are not used.
compileTemplateFile :: FilePath -> IO (Either String Template) Source #
Compile a template from a file. IO errors will be raised as exceptions; template parsing errors result in Left return values.
applyTemplate :: (TemplateMonad m, TemplateTarget a, ToContext b a) => FilePath -> Text -> b -> m (Either String a) Source #
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.
class Monad m => TemplateMonad m where Source #
A TemplateMonad defines a function to retrieve a partial
(from the file system, from a database, or using a default
value).
Methods
getPartial :: FilePath -> m Text Source #
Instances
| TemplateMonad IO Source # | |
Defined in Text.DocTemplates.Internal | |
| TemplateMonad Identity Source # | |
Defined in Text.DocTemplates.Internal | |
class Monoid a => TemplateTarget a where Source #
A type to which templates can be rendered.
Instances
| TemplateTarget Text Source # | |
| IsString a => TemplateTarget (Doc a) Source # | |
A Context defines values for template's variables.
Instances
| Functor Context Source # | |
| Foldable Context Source # | |
Defined in Text.DocTemplates.Internal Methods fold :: Monoid m => Context m -> m # foldMap :: Monoid m => (a -> m) -> Context a -> m # foldr :: (a -> b -> b) -> b -> Context a -> b # foldr' :: (a -> b -> b) -> b -> Context a -> b # foldl :: (b -> a -> b) -> b -> Context a -> b # foldl' :: (b -> a -> b) -> b -> Context a -> b # foldr1 :: (a -> a -> a) -> Context a -> a # foldl1 :: (a -> a -> a) -> Context a -> a # elem :: Eq a => a -> Context a -> Bool # maximum :: Ord a => Context a -> a # minimum :: Ord a => Context a -> a # | |
| Traversable Context Source # | |
| Show a => Show (Context a) Source # | |
| Semigroup (Context a) Source # | |
| Monoid (Context a) Source # | |
| ToContext (Context a) a Source # | |
A variable value.
Instances
| Functor Val Source # | |
| Foldable Val Source # | |
Defined in Text.DocTemplates.Internal Methods fold :: Monoid m => Val m -> m # foldMap :: Monoid m => (a -> m) -> Val a -> m # foldr :: (a -> b -> b) -> b -> Val a -> b # foldr' :: (a -> b -> b) -> b -> Val a -> b # foldl :: (b -> a -> b) -> b -> Val a -> b # foldl' :: (b -> a -> b) -> b -> Val a -> b # foldr1 :: (a -> a -> a) -> Val a -> a # foldl1 :: (a -> a -> a) -> Val a -> a # elem :: Eq a => a -> Val a -> Bool # maximum :: Ord a => Val a -> a # | |
| Traversable Val Source # | |
| FromContext a (Val a) Source # | |
| Show a => Show (Val a) Source # | |
class FromContext a b where Source #
The FromContext class provides functions for extracting
values from Val and Context.
Minimal complete definition
Instances
| FromContext a a Source # | |
| FromContext a [a] Source # | |
| FromContext a (Val a) Source # | |
A template.