logics is a domain-specific, embeddable expressional language with a Python-style syntax. vistache provides a customizable template language and engine powered by logics expressions.
The initial intention behind logics was to serve a well-known syntax for expressing validity checks across all ViUR modules and its execution platforms. This starts from the administration tools to server-side input checking as well as client-side input forms and user-defined template processing.
The first version of logics was intended to allow both direct expression execution and expression compilation into native JavaScript code, to be executed on the client without the need of a logics interpreter. This feature has been disabled for now, but may be re-implemented in the future when needed.
logics is not intended to be a scripting language! Therefore it neither provides direct variable assignment, nor control structures like loops or jumps - except for comprehensions.
Rather than that, it is a language and tool for...
- ...expressing validity checks,
- ...performing custom calculations,
- ...providing customizable templating features,
- ...making data-driven decisions in a restricted and secure runtime context.
logics.py can be used as a command-line tool for invocation and testing.
usage: logics.py [-h] [-D] [-e] [-v var value] [-r] [-V] expression
ViUR Logics Expressional Language
positional arguments:
expression The expression to be processed
optional arguments:
-h, --help show this help message and exit
-D, --debug Print debug output
-e, --environment Import environment as variables
-v var value, --var var value
Assign variables
-r, --run Run expression using interpreter
-V, --version show program's version number and exit
The logics parser is implemented using the UniCC parser generator and its newly established Python support. Install UniCC as instructed in its README, or download a setup for your platform. Then, run make to build the logics parser.
Literals
"Hello World"
2016
23.5
True
[1,2,3]Simple arithmetic expressions
23 / 5 + (1337 - 42)Concatenate current content of a field (variable) with a string literal
myfield + " is my value!"Add enforced string content lengths of two fields firstname and lastname and test them for a total length greater than 32 characters
len(str(firstname)) + len(str(lastname)) > 32Check if current content of field (variable) named degree is filled,
and mother or father, or current integer value of field age is
greater-equal 21 and lower-equal 42.
(degree and degree in ["mother", "father"]) or (int(age) >= 21 and int(age) <= 42)Comprehensions are supported as well
sum([x for x in [10, 52, 18.4, 99, 874, 13, 86] if x > 25]) # Sum all values higher 25The latest versions of ViUR vi support logics to dynamically change input mask behavior depending on input data.
The logics expressions are triggered on an event base, when input field contents are changed.
The following events are supported so far:
logic.visibleIfsets the field visible when the expression returnsTruelogic.readonlyIfsets the field read-only when the expression returnsTruelogic.evaluatesets the field's value according to the provided expression
The expressions are provided by extending skeleton bones to specific expressions on the particular event.
class fieldSkel(Skeleton):
type = selectBone(
descr="Type",
values={
"none": u"None",
"text": u"Text (single line)",
"memo": u"Text (multi-line)",
"select": u"Selection field"
},
required=True, defaultValue="level"
)
value = stringBone(
descr="Default value",
params={"logic.visibleIf": 'type != "none"'}
)
entries = stringBone(
descr="Possible values",
params={"logic.visibleIf": 'type == "select"'},
multiple=True
)
required = booleanBone(
descr="Required",
params={"logic.visibleIf": 'type in ["text", "memo"]'},
defaultValue=False
)
multiple = booleanBone(
descr="Multiple entries",
params={"logic.visibleIf": 'type in ["text", "memo", "select"]'},
defaultValue=False
)
Vistache is built on top of logics, providing an easy-to-use template language with a Mustache-inspired syntax. Similar to the original Mustache, a template is first compiled into an executable representation, then it can be rendered with variable data.
Instead of just outputting variables and performing conditional or iterative blocks, Vistache allows to use full logics expressions as shown in the example below.
Vistache expressions:
{{expression}}just renders the result of expression{{#expression}}...{{/}}renders the block between{{#expression}}and the{{/}}if the expression validates to true. It also loops over the block when the expression results in a list, with a context-related sub-scoping.{{#expression}}...{{|}}...{{/}}renders the block between the{{#expression}}and the{{|}}if the expression validates to true, otherwise it renders the block between the{{|}}and{{/}}. It also loops over the first block when the expression results in a list, with a context-related sub-scoping.{{#expression}}...{{|other-expression1}}...{{|other-expression2}}...{{|}}...{{/}}a variant of an if-elseif-elseif-else-construct.
In case of a loop in the conditional blocks above, a variable loop is also made available in each scope, containing the following members:
loop.lengthis the number of items that are looped,loop.itemis the full context-based variable,loop.indexis the loop conter starting at 1,loop.index0is the loop conter starting at 0,loop.firstis true on the first loop,loop.lastis true on the last loop.loop.parentpoints to the previous loop block variable (None on outer loop)
This feature is inspired by the Jinja2 template engine.
Running the template
{{#persons}}Hello {{firstname}}
{{#city}} from {{city}}{{/}}!
{{# dogs and len(dogs) }}
You have {{len(dogs)}} dog{{ "s" if len(dogs) > 1 else "" }} named
{{#dogs}}
{{#loop.last and not loop.first}} and
{{/}}
{{loop.item}}
{{#loop.index < len(dogs) - 1}},
{{/}}
{{/}}
{{|}}
There is no dog living with you.
{{/}}
{{/}}
with the JSON object
[
{
"firstname": "John",
"city": "Johannesburg"
},
{
"firstname": "Bernd",
"dogs": ["Doge"]
},
{
"firstname": "Max",
"city": "Dortmund",
"dogs": ["Shugar", "Kira", "Akela"]
}
]results in the following output:
Hello John from Johannesburg!
There is no dog living with you.
Hello Bernd!
You have 1 dog named Doge
Hello Max from Dortmund!
You have 3 dogs named Shugar, Kira and Akela
Try it out by calling
python vistache.py -v persons persons.json -r persons.vistachefrom a command-line.
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ViUR is developed and maintained by Mausbrand Informationssysteme GmbH, from Dortmund in Germany. We are a software company consisting of young, enthusiastic software developers, designers and social media experts, working on exciting projects for different kinds of customers. All of our newer projects are implemented with ViUR, from tiny web-pages to huge company intranets with hundreds of users.
Help of any kind to extend and improve or enhance this project in any kind or way is always appreciated.
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Mausbrand and ViUR are registered trademarks of Mausbrand Informationssysteme GmbH.
You may use, modify and distribute this software under the terms and conditions of the GNU Lesser General Public License (LGPL). See the file LICENSE provided within this package for more information.