EVAL operator

The EVAL operator: creating an action that executes code in the lsFusion language.

Syntax

EVAL [ACTION] expression [PARAMS paramExpr1, ..., paramExprN]

Description

The EVAL operator is designed to execute program code while the server is running. The operator takes as its argument a string containing source code. This string can be a simple string constant or a more complex expression that evaluates to a string.

The code that is passed should consist of a sequence of statements (or action operators and local property declarations, if the ACTION option is specified). When the action is executed, this code is inserted into a module with a unique name. The module header is generated by the system: it declares a unique name for the module and lists all the modules that are in the project in the REQUIRE statement. Thus, you can use all elements from other modules in the code passed in the EVAL operator. If the ACTION option is not specified, it is assumed that one of the passed statements will be the creation of action with the name run (it is this action that will be executed).

Parameters

• expression

  An expression whose value is the string to be executed.

• ACTION

  Keyword.

• paramExpr1, ..., paramExprN

  A list of expressions whose values will be passed to the action being executed as arguments. The number of expressions must be equal to the number of parameters of the action being executed.

Examples

// source code consisting of one statement is specified with a string constant
addProperty  { EVAL ACTION 'MESSAGE \'Hello World\''; }  

// a property to which the user can enter the source code
code 'Source code' = DATA BPSTRING[2000] ();

// the action executing this code              
execute 'Execute code'  { EVAL code(); }