A simple string template library with runtime template loading.
Note that runtime loading of templates prevents static checks of template (for invalid references, or invocation of a value of the wrong type. In such cases the library will produce the best output it can and a list of errors.
In all contexts, Stencil reserves doubled and tripled angle brackets with an internal parenthesis ('<<(', ')>>') and pipes ('|'). If any of these are needed within the text, add one angle bracket or two pipes, as appropriate: '<<<(' becomes '<<(', '|||' '|', '|||| '||', and so on. For simplicity, these should be escaped everywhere, not merely where syntactically significant.
Variable names must start with a letter and otherwise contain only letters, numbers, underscores, and apostrophes.
<<(name)>>
Substitute the value of name (which should be text or a Haskell value with a defined conversion to text) from the present context. In all substitutions, doubling the parentheses (<<((name))>>) results in the contained text being HTML escaped.
<<(?name| text1 | text2 )>>
If name is in the dictionary and is not the boolean False, substitute text1; otherwise substitute text2.
<<(%name| text )>>
Evaluate text in the context of the dictionary referred to by name. Within text, any lookups not found in that dictionary are passed to the next higher context.
<<(@name| text | alternate text )>>
Substitute text for each item of the list referred to by name. If name is a list of texts, they can be accessed with '<<()>>' within text, so that <ul><<(@listname| <li> <<()>> </li> )>></ul> becomes <ul> <li> item1 </li> <li> item2 </li> </ul>. If the list is empty, substitute the alternate text if present. if name refers to a list of dictionaries, each evaluation of text is in the context of the corresponding dictionary.
<<(!functionname| valuename )>>
Substitute the result of applying the function to the value. Note that arbitrary Haskell is not allowed; the function used must be explicitly placed in the dictionary.
<<($functionname| text )>>
Substitute the result of applying the function to the text, after making substitutions within the text.
<<(&templatename)>>
Substitute and evaluate the named template.