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Expr Block ​

The expr block is space for evaluating standard PKL expressions. It is primarily used to execute expressions that produce side effects, such as updating resources or triggering actions, but also supports general-purpose evaluation of any valid PKL expression, making it a place for inline logic and scripting within a configuration.

Overview of the expr Block ​

The expr block is designed to evaluate PKL expressions in a straightforward manner. Its key uses include:

  • Side-Effecting Operations: Executing functions like memory.setRecord that modify resources or state without returning significant values.

  • Inline Scripting: Evaluating arbitrary PKL expressions to implement logic, assignments, or procedural tasks directly within a configuration.

The expr block simplifies the execution of side-effecting operations that does not makes sense to output it's results.

Syntax and Usage ​

The expr block is defined as follows:

apl
expr {
  // Valid PKL expression(s)
}

Each expression within the block is evaluated in sequence, allowing multiple expressions to form a procedural sequence if needed.

The expr block is well-suited for operations that update state, such as setting memory items.

apl
expr {
  "@(memory.setRecord("status", "active"))"
}

In this example, the memory store is updated to indicate an active status. The memory.setRecord function is executed as a side effect, and no return value is required. This also applies to memory.clear().