POP-2 Language Features ALGOL-like Syntax with Concatenative Evaluation

Syntax and Evaluation

POP-2 integrates an ALGOL-like syntax for its structure, including infix notation for assignments. However, its evaluation mechanism is deeply concatenative, relying on an explicit operand stack. For example, an assignment like `123 -> foo;` can be broken down into two statements: `123;` which pushes a value onto the stack, and `-> foo;` which consumes it.

Interpreter Efficiency

The language's design allows for a highly efficient interpreter. A compiler for POP-2 targeting Uxn is notably small, consisting of less than 800 lines of code and occupying only 2.5kb of memory. This demonstrates the language's elegance and compact nature.

Core Language Constructs

POP-2 statements begin with keywords, followed by expressions, and are terminated by a semicolon, resembling Pascal. Evaluation progresses by placing values onto the stack as needed. Functions, declared in an ALGOL fashion, handle recursion by leaving arguments on the stack. Control flow includes `if/then/elseif/else/close` statements, where each case pushes a value onto the stack rather than returning a value or performing an assignment. Loops are implemented using simple `GOTO` statements, as there are no built-in iterators.

Variable and I/O Handling

Variables are allocated using a `vars` statement and can be of varying lengths; in a 16-bit system, a variable defaults to two 8-bit cells. Comments are block-style, spanning text until a terminating semicolon. For I/O, the language, when implemented on the Varvara host system, can utilize multiple output destinations, such as outputting ASCII characters to console port numbers.