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;
}