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Template-Plex-v0.1.1
River stage one • 2 direct dependents • 3 total dependents
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/ Template::Plex

NAME

Template::Plex - Templates in (P)erl using (Lex)ical Aliasing

SYNOPSIS

        use Template::Plex;

        #Data for templates to alias and access
        my $base_data={
                name=>"James",
                age=>"12",
                fruit=>"banana"
        };


        #The actual template text
        #
        my $inline_template='$name\'s age $age and favourite fruit is $fruit'

        #Preparing the template in Template::Plex object
        #
        my $t=plex [$inline_template], $base_data, %options;


        #Render with the values aliased in $base_data
        $t->render;
        #
        #=>     James's age is 12 and favourite fruit is banana

        #Update the data in the hash used during preparation.
        #
        $base_data->{qw<name,fruit>}=qw<John apple>;


        #Rendering again will use updated aliased values
        #
        $t->render;
        #
        #=>     John's age is 12 and favourite fruit is apple

DESCRIPTION

This module is a mechanism to facilitate the use of perl (not embedded perl) as a text processing template language.

Conceptually, a Template::Plex template is just a string returned from a subroutine in perl's double quoted context, with the outer operators removed:

        #PERL
        "This is is a perl string interpolating @{[ map uc, qw<a b c d>]}"

        #  or

        qq{This is is a perl string interpolating @{[ map uc, qw<a b c d>]}}
        

        #PLEX template. Same as PERL syntax, without the outer double quotes
        This is is a perl string interpolating @{[ map uc, qw<a b c d>]};

        #OUTPUT is the same for all of the above:
        This is is a perl string interpolating A B C D

Because of the powerful and flexible interpolation of strings in perl, you can do just about anything in a Plex template. After all the template is just perl.

The 'lexical' part of this modules refers to ability of variables to be aliased into the template (more on this later). It improves the style and usage of variables in a template while also allowing sub templates to access/override variables using lexical scoping.

Some feature highlights:

  • Templates are written in perl syntax

  • Templates are compiled into a perl subroutine

  • Lexical and package variables accessed/created within templates

  • Call and create subroutines within templates

  • 'Include' Templates within templates easily

  • Recursive and conditional sub template loading

  • Declare variables and subroutines in templates

  • use other modules directly in templates

To get started after installation, copy the following lines into perl and execute:

        use strict;
        use warnings;
        use feature "say";
        use Template::Plex;
        my %vars=(name=>"Susan", age=>99);
        my $template=plex ['this is ${name}\'s inline template. $age young'], \%vars;
        say $template->render;
        
        @vars{qw<name age>}=qw<Richard 23>;
        say $template->render;

For more examples, checkout the examples directory in this distribution.

MOTIATION

  • So many templating systems available, yet none use perl as the template language?

  • Lexical aliasing allows the input variables to be accessed directly by name (i.e. $name) instead of as a member of a hash ref (i.e. $fields->{name}) or by delimiting with custom syntax (i.e. <%= name %>)

  • The perl syntax @{[...]} will execute arbitrary perl statements in a double quoted string.

  • Other templating system are very powerful, but have huge a huge APIs and options. Template::Plex could have a very minimal API with perl doing the hard work

TODO

  • More tests

  • Add a guide document

  • CLI app to render .plex files

  • Fix any bugs

API

plex

        plex $path, $variables_hash, %options

Creates a new instance of a template, loaded from a scalar, file path or an existing file handle.

Multi Argument Version

If 2 or more arguments are provided, the template is loaded and prepared and returned. The returned template can be rendered by calling the render method on it.

Single Argument Version

If only the first argument is supplied, the template is loaded, prepared, and rendered immediately. The rendered text is returned. This is useful when using sub templates, as the variables and options are already available from the top level template.

The arguments are detailed below:

$path

This is a required argument.

If $path is a string, it is treated as a file path to a template file. The file is opened and slurped with the content being used as the template

If $path is filehandle, or GLOB ref, it is slurped with the content being used as the template. Can be used to read template stored in __DATA__ for example

If $path is an array ref, the items of the array are joined into a string, which is used directly as the template.

$variables_hash

This is an optional argument but if present must be an empty hash ref {} or undef.

The top level items of the $variables_hash hash are aliased into the template using the key name (key names must be valid for a variable name for this to operate). This allows an element such as $fields{name}> to be directly accessible as $name.

It also means any external modification of the items in $variable_hash will be visible in the template.

In addition, the $variables_hash itself is aliased to %fields variable (note the %) and directly usable in the template like a normal hash e.g. $fields{name}

If the $variables_hash is an empty hash ref {} or undef then no variables will be lexically aliased. The only variables accessible to the template will be via the render method call

Options

These are non required arguments, but must be key value pairs when used.

Options are stored lexically in the rendering sub in the variable %options for recursive plex calls within a template.

Currently supported options are:

root

root is a directory path, which if present, is prepended to to the $path parameter if $path is a string (file path).

no_include

Disables the uses of the preprocessor include feature. The template text will not be scanned and will prevent the include feature from operating. See include for more details

This doesn't impact recursive calls to plex when dynamically/conditionally loading templates.

package

Specifies a package to run the template in. Any our variables defined in the template will be in this package. If a package is not specified, a unique package name is created to prevent name collisions

Return value

The return value is Template::Plex object which can be rendered using the render method

Example Usage my $hash={ name=>"bob", age=>98 };
                my $template_dir="/path/to/dir";

                my $obj=plex "template.plex", $hash, root=>$template_dir;

render

        $obj->render($fields);

This object method renders a template object created by plex into a string. It takes an optional argument $fields which is a reference to a hash containing field variables. fields is aliased into the template as %fields which is directly accessible in the template

        eg
                my $more_data={
                        name=>"John",
                };
                my $string=$template->render($more_data);
                
                #Template:
                My name is $fields{John}

Note that the lexically aliased variables in plex are independent to the %fields variable and can both be used simultaneously in a template

include

        @{[include("path")}]

        where $path is path to template file to inject

Used in templates only.

This is a special directive that substitutes the text @{[include("path")]} with the contents of the file pointed to by path. This is a preprocessing step which happens before the template is prepared for execution

This API is only available in templates. If root was included in the options to plex, then it is prepended to path if defined.

When a template is loaded by plex the processing of this is subject to the no_include option. If no_include is specified, any template text that contains the @{[include("path")}] text will result in a syntax error

PLEX TEMPLATE SYNTAX \w EXAMPLES

Well, its just perl. Seriously. But if you haven't grasped the concept just yet, a Template::Plex template is a perl program with the two following constraints:

  • consists only of perl syntax permissible in a double quoted string

  • outermost double quote operators are ommited from the program/template

This is best illustrated by example. Suppose the following text is stored in a file or in the __DATA__ section:

        The pot of gold at the end of the rainbow has $amount gold coins
        As for the rainbow, the colors are:
        @{[ map ucfirst."\n", @$colors ]}
        Good day!

Everything in the text is valid syntax in double quote operator, but the outer double quote operator is omitted.

Or in other words, the template looks like plain text, but with double quoted added, it is valid perl code.

Neat!

Following sections show example of particular scenarios

Access to Existing Scalars, Arrays and Hashes

If $variables_hash was supplied during a plex call, the top level elements will be aliased and accessible as normal scalars in the template.

        This template uses a scalar $name that was lexically aliased
        Here the same variable can be accessed via $fields{name}        
        Calling render with an hash argument will override the $fields{name}
        AReallylong${word}WithAVariable

        access the array element $array->[$index]
        Accessing element $hash->{key} just for fun

Executing a single (or list) of Statements

To achieve this, a neat trick is to dereference an inline reference to an anonymous array. That is @{[...]}. The contents of the array is then the result of the statements. Sounds like a mouthful, but it is only a couple of braces and lets you do some powerful things:

        Calling a subrotine @{[ my_sub() ]}
        Doing math a + b = @{[ $a+$b ]}
        Building an array @{[ uc("red"),uc("blue")]}
        Mapping @{[ join "\n", map uc, @items]}

Executing Multiple Statements

When a single statement won't do, the do{} construct executes a block, which can have any number of statements and returns the last statement executed into the template

        Executing multiple statments @{[ do {
                my $a=1; 
                $a++; 
                ($a,-$a)

        } ]} in this template

Using/Requiring Modules

Again standard perl syntax for the win

        Template will call hi res time 
        The time is: @{[ time ]}
        @{[ do {
                BEGIN {
                        use Time::HiRes qw<time>;
                }
        }
        ]}

Declaring Variables

Variables can be declared in the @{[..}] container.

my variables will only be visible within the @{[..]} block it was defined.

        eg      #render a mini single line template with my variable
                @{[ do {
                        my $a=time;
                        $a+=23;
                        "Time is: $a";  
                } }]

our variables can be used instead of my variables and are visible throughout the current template, including recursively used templates

        eg
                @{[ do {
                        our $a=time;
                        "";
                } }]
                
                Template package variable is $a

                @{[ do {
                        $a+=23:
                        ""
                } ]}
                Updated template package variable is $a

Sub templates loaded with include and recursive plex calls will have direct access to package variables created in the template. A new unique package is created for each top level use of plex to prevent name collisions.

TIPS ON USAGE

Points to note

  • Aliasing is a two way steet

    Changes made to aliased variables external to the template are available inside the template (one of the main tenets of this module)

    Changes make to aliased variables internal to the template are available outside the template.

  • Unbalanced Delimiter Pairs

    Perl double quote operators are smart and work on balanced pairs of delimiters. This allows for the delimiters to appear in the text body without error.

    However if your template doesn't have balanced pairs (i.e. a missing "}" in javascript/c/perl/etc), the template will fail to compile and give a strange error.

    If you know you don't have balanced delimiters, then you can escape them with a backslash

    Currently Template::Plex delimiter pair used is { }. It isn't changeable in this version.

  • Are you sure it's one statement?

    If you are having trouble with @{[...]}, remember the result of the last statement is returned into the template.

    Example of single statements

            @{[time]}                       #Calling a sub and injecting result
        @{[$a,$b,$c,time,my_sub]}       #injecting list
        @{[our $temp=1]}                #create a variable and inject 
        @{[our ($a,$b,$c)=(7,8,9)]}     #declaring a

    If you are declaring a package variable, you might not want its value injected into the template at that point. So instead you could use do{..} execute multiple statements, with the last statement being an empty string (or the value you want returned into the template).

            @{[ do {our $temp=1;""} }];

  • Last newline of templates are chomped

    Most text editors insert a newline as the last character in a file. A chomp is performed before the template is prepared to avoid extra newlines in the output when using sub templates. If you really need that newline, place an empty line at the end of your template

More on Input Variables

If the variables to apply to the template completely change (note: variables not values), then the aliasing setup during a plex call will not reflect what you want.

However the render method call allows a hash ref containing values to be used. The hash is aliased to the %fields variable in the template.

        my $new_variables={name=>data};
        $template->render($new_variables);

However to use this data the template must be constructed to access the fields directly:

        my $template='my name is $fields{name} and I am $fields{age}';

Note that the %field is aliased so any changes to it is reflected outside the template

Interestingly the template can refer to the lexical aliases and the direct fields at the same time. The lexical aliases only refer to the data provided at preparation time, while the %fields refer to the latest data provided during a render call:

        my $template='my name is $fields{name} and I am $age

        my $base_data={name=>"jimbo", age=>10};

        my $override_data={name=>"Eva"};

        my $template=plex $template, $base_data;

        my $string=$template->render($override_data);
        #string will be "my name is Eva and I am 10

As an example, this could be used to 'template a template' with global, slow changing variables stored as the aliased variables, and the fast changing, per render data being supplied as needed.

SECURITY

This module uses eval to generate the code ref for rendering. This means that your template, being perl code, is being executed. If you do not know what is in your templates, then maybe this module isn't for you.

Aliasing means that the template has access to variables outside of it. That's the whole point. So again if you don't know what your templates are doing, then maybe this module isn't for you

SEE ALSO

Yet another template module right?

Do a search on CPAN for 'template' and make a cup of coffee.

REPOSITORY and BUG REPORTING

Please report any bugs and feature requests on the repo page: GitHub

AUTHOR

Ruben Westerberg, <drclaw@mac.com>

COPYRIGHT AND LICENSE

Copyright (C) 2022 by Ruben Westerberg

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, or under the MIT license