MVEL

Infobox_Software
name = MVEL



caption =
developer = Mike Brock and Various Contributors
latest_release_version = 1.3.13
latest_release_date = release_date|2008|10|10
latest_preview_version = 2.0 Beta 1
latest_preview_date = release_date|2008|10|03
operating_system = Cross-platform
programming_language = Java
genre = Expression Language (EL)
license = Apache License
website = http://mvel.codehaus.org

MVFLEX Expression Language (MVEL) is a hybrid dynamic/statically typed, embedable Expression Language and runtime for the Java Platform. Originally started as a utility language for an application framework, the project is now developed completely independently.

MVEL is typically used for exposing basic logic to end-users and programmers through configuration such as XML files or annotations. It may also be used to parse simple JavaBean expressions.

The runtime allows MVEL expressions to be executed either interpretively, or through a pre-compilation process with support for runtime bytecode generation to remove overhead.

Since MVEL is meant to augment Java-based software, it borrows most of its syntax directly from the Java programming language with some minor differences and additional capabilities. For example: as a side-effect of MVEL's typing model, which treats class and method references as regular variables, it is possible to use both class and function pointers (but only for static methods).

millis = System.currentTimeMillis;

// get millis time = millis();

MVEL also allows collections to be represented as folds (or projections) in a Lisp-like syntax.

namesOfParents = (parent.name in (children in employees));

Hello world example

System.out.println("Hello, world!");

MVEL relies on Java namespaces and classes, but does not possess the ability to declare namespaces or classes. In this sense, MVEL is a completely functional language.

MVEL 2.0

The next version of MVEL 2.0, which is still in development stage supports more features, enabling it as a more full-fledged scripting language. Here is an example of the Quicksort algorithm implemented in MVEL 2.0

array = null;

def swap(i, j) { temp = array [i] ; array [i] = array [j] ; array [j] = temp;}

def partition(low, high) { pivotPoint = array [low] ;

i = low - 1; j = high + 1;

while (i < j) { i++; while (array [i] < pivotPoint) ++i; j--; while (array [j] > pivotPoint) --j; if (i < j) swap(i, j); }

j; //return j}

def sort(low, high) { if (low < high) { var p; sort(low, p = partition(low, high)); sort(p + 1, high);

def quicksort() { sort(0, array.length - 1);}

array = {50,20,21,209,10,77,8,9,55,73,41,99};

quicksort();

ee also

* Java
* OGNL
* Expression Language

Links

* [http://mvel.codehaus.org/Language+Guide MVEL Language Guide]