A tiny templating language for writing email generation conventions.

Writing a Template

The Template Structure

A Hafr template consists of two different parts: text and holes. Text is just literal text that will be output verbatim when evaluating the template against a model. A hole will be filled in based on its contents and the model during evaluation. Here's an example:

Hello {name}!

The first and last parts, Hello and ! are literal text, while {name} is a hole. Inside holes, you can access public properties of the model you're evaluating against. If you have the following class:

public record Person(string Name);

And evaluate the template against the following instance:

var person = new Person("John Doe");

The template above will yield:

Hello John Doe!

Any public property of the model will be exposed to the template.

Calling Functions

Hafr has a few built-in methods that you can call to transform properties inside holes:

Method	Description
split	Takes a separator argument to split its input into separate parts.
join	Takes a separator argument to join several parts into one.
substr	Takes a count argument to extract a specified number of characters for each part.
skip	Takes a count argument to skip a specified number of parts.
take	Takes a count argument to pick a specified number of parts.
replace	Takes a string to replace and its replacement value.
reverse	Reverses a string or a list of strings.
upper	Converts a string to uppercase.
lower	Converts a string to lowercase.
trim	Trims whitespace from the start and end of a string.
truncate	Truncates a string to the specified max length.

These methods can be called in one of two ways; using C-style function calls:

Hello {join(split(name, ' '), '.')}!

...or using piping:

Hello {name | split(' ') | join('.')}!

Parsing a Template

To parse a template, use the Parser.TryParse method:

var template = "{firstName | split(' ') | join('.')}.{lastName}@company.com";

if (Parser.TryParse(template, out var expression, out var errorMessage, out var errorPosition))
{
    // Parsing succeeded, it's safe to access the expression in here...
}
else
{
    // Parsing failed. You can use errorMessage and errorPosition in here...
}

Evaluating a Template

After the template has been successfully parsed, you can use it to evaluate against an input model:

public record Person(string FirstName, string LastName);

var model = new Person("John Michael", "Doe");

var result = expression.Evaluate(model).ToLower(); // john.michael.doe@company.com