mhtemplate

mhtemplate is an easy-to-use, dynamic text template library.

Usage

[dependencies]
mhtemplate = "1"

extern crate mhtemplate;

use mhtemplate::{Context, TemplateFactory};

let text = include_str!("text.template");
let tmpl = TemplateFactory::new(&text).parse().unwrap();
let text = tmpl.evaluate(&mut Context::new()).unwrap();

Changelog

lib.rs:

Text template library.

A template is a text which may contain special delimiters:

• Statements: {% ... %}
• Expression: {{ ... }}
• Comments: {# ... #}

A hyphen may be added to any delimiter, {%- or -%}, to remove leading or trailing whitespace, respectively.

Expressions

Template expressions may consist of constants, variables and operators. There are no concept of operator precedence, and evaluation are done right to left. However, this may change in future releases.

Expressions occur inside expression delimiters: {{ ... }} or some statements, and may be evaluated as string, number or boolean, depending on context.

Supported expressions:

Expressions evaluated as booleans will evaluated as:

• Number: "0" is false, anything else is true.
• "true"/"false" strings (case insensitive) is true/false.
• A comparison expression which returns true/false.
• Anything else is false.

Statements

Statements occur inside statement delimiters: {% ... %}. Supported statements are loops, conditionals, set and with.

Loops

A repeat loop:

{% repeat <expr> %}
Hello
{% end %}

A for loop:

{% for <ident> in <expr> %}
Hello {{ $<ident> }}
{% end %}

A enumerated for loop:

{% for <ident_i>, <ident> in <expr> %}
Hello {{ $<ident> }} (element nr. {{ $<ident_i> + 1 }})
{% end %}

Expressions in loops are evaluated as numbers or strings. As number the loop will iterate over [0,n). As a string the loop will iterate over the words in the string, split at whitespaces.

Conditionals

if/elif/else conditional:

{% if <expr> -%}
    Hey if
{% elif <expr> -%}
    Hey elif
{% else -%}
    Hey else
{% end %}

Any expression in a conditional statement are evaluated as boolean.

Context

A context is passed to a template during evaluation, which may contain values of variables available during evaluation.

A context may be created from a HashMap or environment variables.

Simple context:

let mut ctx = Context::new();
ctx["NUMBER"] = String::from("42");

Context from environment:

let vars = std::env::vars();
let ctx  = Context::from(vars);

Example

Template text:

{% set num 4
   set str Hello World %}

{%- repeat $num -%}
Brrapp {% end %}

{%- for VAL in $num -%}
{{ $VAL }}
{% end %}

{% for i, s in $str -%}
{{ $i }} - {{ $s }}
{%end%}

{%- if $num > 6 %}
NOT PRINTED
{%- elif $num == 4 %}
PRINTED
{%- else %}
NOT PRINTED
{%- end %}


{%- with
   set num (($num*2) - 1)--
   set str UGH %}
Ut enim ad minim {{ $str }}, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. 

Duis aute irure dolor in reprehenderit in voluptate velit {{ $num }} cillum dolore eu fugiat nulla pariatur.
{% end -%}

Excepteur sint occaecat cupidatat non {{ $str }}, sunt in culpa qui officia deserunt mollit anim id est {{ $num }}.

Rust unsage:

let text = String::from("{% repeat 3 %} Hello {% end %}");
let tmpl = TemplateFactory::new(&text).parse().unwrap();
let text = tmpl.evaluate(&mut Context::new()).unwrap();

The evaluated template returns:

Brrapp Brrapp Brrapp Brrapp 0
1
2
3


0 - Hello
1 - World

PRINTED
Ut enim ad minim UGH, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

Duis aute irure dolor in reprehenderit in voluptate velit 6 cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non Hello World, sunt in culpa qui officia deserunt mollit anim id est 4.