POP-11 programming is a reflective, incremental programming language that combines some of the characteristics of both an interpreted and compiled language. The programmer creates expressions, which are interpreted, and the computer evaluates these expressions and produces results. The generated code is then placed into a program.

An expression can be a single string, or it can consist of multiple strings joined together in the right order. The code generated is either executed right away or stored for later evaluation. An expression is executed when the program starts up. If a program does not load, execution of the expression fails.

An expression is evaluated at most once per instruction, called instruction cycle. Each instruction has two operands; the first operand is the constant value. This constant value is used by the interpreter to perform all the evaluation on the expression. The interpreter does not have access to any information from previous instructions. Therefore, the constant value is accessed directly by the programmer.

When a program is executed, instructions are used to process each expression and store the result in a variable. Some instructions use a label to store the result and others use a pointer. The interpreter can store the result in a register.

An expression is often used as a way to store temporary or static information, such as function arguments, variable names, and return address. These data structures are available to the program only if they are evaluated when the program is started up.

To evaluate an expression, a series of instructions called operators is used. The operators are the left and right side of an operator, such as +, -, *, and /.

The left side of an operator, called operand, is an expression that must be evaluated before the right side of the operator. There are two types of operators; left associative and right associative. An operator is either associative if the operator performs the left side of an operation and the right side is the result; or it is right associative if the operator performs the right side and the left side is the result. In left associative operator, the left operand is evaluated and the result is stored, while in right associative operator, the left operand is evaluated and then the result is stored.

An expression can be stored in registers. When a program is finished, the register containing the expression that was stored is released. When it is called for the first time, an instruction that is equivalent to the expression is written to store in the register.

The program executes instructions with labels. Every label that is encountered by the interpreter is used to store the value of the expression or the result of the previous expression.

If an instruction is not immediately needed, it is written to a register. After that, the expression is not needed so the label is written. to the register and the instruction is executed.

The expression is used to do multiple operations at once. The expression can be used as an arithmetic operator, as a variable, and as an operator.

Another important feature of an expression is the ability to store or return an expression in a variable. If you want to store an expression into a variable, you can write the expression in a register. and the statement is executed.

The expression can also be used as a return type or as a place holder for a label. If you want to store a variable to a label, you have to write the expression in a register before using it as a return type. The expression will be stored and the expression will be automatically returned when the label is accessed. when the label is called for the first time.

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