EVAL operator

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

Syntax

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

Description

The string produced by expression is wrapped by the platform into a uniquely-named module whose dependencies cover every loaded module of the project, then executed. Without ACTION the code is treated as a sequence of statements; one of those statements must declare an action named run, which is the action that gets executed. With ACTION the code is treated as the body of run directly — a sequence of action operators and local property declarations — and runtime arguments are addressed positionally as $1, $2, ....

Runtime arguments are supplied via the optional PARAMS block — a list of expressions whose values are passed to run as positional arguments. Without PARAMS run is invoked with no arguments.

Parameters

• ACTION

  Optional keyword. When specified, the source code is taken as the body of run directly, rather than as a sequence of statements that declares it.

• expression

  An expression whose value is the source code string to be executed.

• paramExpr1, ..., paramExprN

  Non-empty list of expressions whose values are passed to run as positional arguments. The count must match the parameter count of run.

Examples

// statements form: the source string declares a `run` action
code 'Source code' = DATA BPSTRING[2000] ();
execute 'Execute code' { EVAL code(); }

// ACTION form: the string is the body of `run` directly
addProperty { EVAL ACTION 'MESSAGE \'Hello World\''; }

// ACTION form with PARAMS — runtime arguments addressed as `$1, $2, ...`
greet 'Greet user' (CustomUser u) { EVAL ACTION 'MESSAGE \'Hello, \' + name($1);' PARAMS u; }

// statements form with PARAMS — values bind positionally to `run`'s parameters
greetByName 'Greet by name' (STRING n) {
    EVAL 'run(STRING name) \{ MESSAGE \'Hello, \' + name; \}' PARAMS n;
}