A few feral cats in an ALGOL trenchcoat.

# pop2 Source: [https://wiki.xxiivv.com/site/pop2.html](https://wiki.xxiivv.com/site/pop2.html) ## A few feral cats in an ALGOL trenchcoat\. The syntax of**POP\-2**is ALGOL\-like, assignments are in the[infix notation](https://wiki.xxiivv.com/site/notation.html), but the evaluation scheme is[deeply concatenative](https://wiki.xxiivv.com/site/concatenative.html)\. ``` foo := 123; ( In Pascal ) ``` ``` 123 -> foo; ( In POP-2 ) ``` The language has the explicit notion of an operand stack\. Thus, the prior assignment can be written as two separate statements where the first one leaves a value on the stack, and the second, consumes it: ``` 123; -> foo; ``` Typical POP\-2 Programmer### Interpreter The language can easily be compiled for[Uxn](https://wiki.xxiivv.com/site/uxn.html), in fact, the language is so elegant and small that an entire compiler is less than 800 lines and fits within 2\.5kb of memory\. At first glance, the language looks a little like[Pascal](https://wiki.xxiivv.com/site/pascal.html)\. A statement begins with a keyword, followed by expressions, terminated by a semi\-colon\. Evaluation consists of moving through the program leaving values on the stack as needed\. ``` function sum x y; x + y; end sum(5,6) * 2; ``` But it's important to remember that everything is evaluated by a stack machine, a function returning multiple values, is merely leaving them on the stack for the next one to use\. ### Comment The comment statement will block out a length of text until a terminating semi\-colon\. ``` comment This is a comment, these can span multiple lines; ``` ### Vars Variables are allocated inside the vars statement, these can be of any length, by default in a 16\-bit system, a variable is made of two 8\-bit cells\. ``` comment These are 3 variables x, y and z; vars x y z; comment The variable foo is 10 bytes long; vars foo:10; ``` ### If/Then/Elseif/Else/Close At first glance, the language looks awfully unsurprising, but notice how each case pushes a value on the stack instead of returning a value or doing an assignment: ``` vars x; 4 -> x; if x > 4 then 1; elseif x = 4 then 2; else 3; close ``` ``` 2 ``` ### Function/End Functions are declared in the typical ALGOL fashion, recursion leaves the arguments on the stack: ``` function factRec n; if n = 0 then 1; else n * factRec(n-1); close end factRec(5); ``` ### Goto Loops are written with simple[GOTOs](https://wiki.xxiivv.com/site/basic.html), there are no iterators\. ``` comment Loop for 10 times; vars i; loop: if i < 10 then i + 1 -> i, goto loop; close i; ``` ``` 10 ``` ### I/O While the original implementation used the big arrow\(=\>\) without a destination, here the host system of this implementing is[Varvara](https://wiki.xxiivv.com/site/varvara.html)and so it can make use of multiple output destinations\. The[Console port](https://wiki.xxiivv.com/site/varvara.html#console)number\(0x17, 0x18\) to output the[ASCII](https://wiki.xxiivv.com/site/ascii.html)letter "H": ``` 0x48 => 23; Outputs: H ``` ### Arrays A variable can hold a length of cells, each cell is a byte, the absolute position of a reference in memory\(a pointer\) is accessed with the\#prefix\. To store the short`0x0048`in the third and fourth cells of the array: ``` vars array:10 i; 2 -> i; 0x48 -> (#array+i); ``` The curlies can enclose pointer arithmetic and load the value at a location in memory\. The big arrow is sending it to the Console port\. ``` {array+i} => 23; ``` Putting it all together, we can make a string printing function: ``` comment The 23 is a port number in Varvara; function putChar c; c => 23; end function printString s; vars c:1 i; 0 -> i; loop: {s+i} >> 8 -> c; if c then putChar(c), i + 1 -> i, goto loop close end printString("Hello World!\n"); ``` - [Source](https://wiki.xxiivv.com/etc/pop2.tal.txt), Uxntal\. - [Repository](https://git.sr.ht/~rabbits/pop2), Uxntal\. - [A Modest Proposal](https://hitogata.neocities.org/POP-2000), intercatlang\. **incoming:**[oscean](https://wiki.xxiivv.com/site/oscean.html)[2026](https://wiki.xxiivv.com/site/2026.html)