Lust

Lua string generator using structured templates.

The basic principle is that a set of templates define a space of possible structures, and these structures can be specialized according to input data (the "model"). At definition time, Lust generates code to implement the templates, resulting in a partially specialized generator function. At application time, this function interpolates the model to produce an output string.

Within template bodies, a variety of special syntax can be used to interpolate model data and sub-templates. All invocations can be wrapped in to avoid ambiguity with inline text.

• Elements from the model can be inserted using $model_path syntax.
• A single period (.) indicates the current environment, otherwise is used to chain path terms, e.g. $a.b.1
• Templates and sub-templates can be invoked using @template_path syntax, including chained terms.
• Paths may include dynamically evaluated terms using parentheses (such as choosing a subtemplate according to a value in the model).
• Invocations of sub-templates can utilze sub-structures in the model, using the @model_path:template_path syntax.
• Conditional items can be inserted using @if, and iterations can be specified using @iter, @map and @rest special forms.
• Subtemplates can be specified using {{ inline }} syntax, rather than by name.
• Lust tries to do the right thing in automatically inserting indentation.
• Arbitrary Lua functions can be registered to modify environment terms for particular subtemplates. (Nevertheless, it is recommended to construct templates/models which avoid computation in the template application if possible).

Basic example

lust = require "lust"

-- a template can be specified as a table of subtemplates:
local template = lust{
	-- first rule is the 'root template':
	"The classic $greeting @typical:place example",
	-- a sub-template:
	place = "$1"
}

-- a data model to apply:
local model = {
	greeting = "hello",
	typical = { "world" }
}

-- the first time gen() is called on a template, it will lazily generate the generator
-- subsequent calls will re-use this generator
-- the argument to gen(), if given, becomes a data model, and the result is the application of the generator and model:
local result = template:gen(model)
assert(result == "The classic hello world example")

Meta

Lust depends on LPeg (http://www.inf.puc-rio.br/~roberto/lpeg/)

Released under the MIT licence (as used by Lua 5.1).

Authored by Graham Wakefield & Wesley Smith, 2012.