Quests

Quests is the first Questa-based made language by User:ChuckEsoteric08.

Syntax

The following Extended Backus-Naur Form (EBNF) describes the language's syntax:

program       := [ command , { whitespaces , command } ] ;
command       := push | pop | increment | output | decrement | swap ;
expression    := integer | string | command ;
push          := "p"   , "(" , expression , ")" ;
pop           := "<"   , "(" , expression , ")" ;
output        := ">"   , "(" , expression , ")" ;
increment     := "inc" , "(" , expression , ")" ;
decrement     := "dec" , "(" , expression , "," , expression , ")" ;
swap          := "sw"  , "(" , ")" ;

string        := textCharacter , { textCharacter } ;
integer       := [ "+" | "-" ] , digit , { digit } ;
whitespaces   := whitespace , { whitespace } ;
whitespace    := " " | "\t" | "\n" ;
textCharacter := letter | digit | "_" | "-" ;
letter        := "a" | ... | "z" | "A" | ... | "Z" ;
digit         := "0" | "1" | "2" | "3" | "4"
              |  "5" | "6" | "7" | "8" | "9" ;

Commands

Command	Function
p(x)	Pushes x to top of the Questa
<(x)	If x is 0, pops the element from the top. If 1, pops the element from the bottom
>(x)	If x is 0, pops the element from the top and outputs it. If 1, pops the element from the bottom and outputs it
inc(x)	If x is 0, increments the element on the top. If 1, increments the element on the bottom
dec(x,y)	If x is 0, jumps to the y-th command if top of the quest is zero and if it isn't decrement top of the questa, with the commands being indexed starting with zero (0). If x is 1 jumps to the y-th command if bottom of the questa is zero and if it isn't decrement bottom of the questa
sw()	Swaps the elements on the top with the element on the bottom

x can't contain spaces, because these are utilized to separate commands.

Examples

Hello World

p(HelloWorld) >(0)

Goto

The following example utilizes the dec command with the purpose of obviating the insertion of an element. After pushing the values “Hello” and 0 unto the Questa, the goto facility bypasses the pushing of the “World” string to its top by using the top 0 element for its navigation, thus popping and returning in the last step the top value 0 instead.

p(Hello)
p(0)
dec(0,4)
p(World)
>(0)

Turing-completness

It is Turing-complete, beacuse it can simulate Szewczyk notation for Minsky machine with 2 registers like that:

MM	Quests
Start	p(0) p(0)
A -1	inc(0)
B -1	inc(1)
A Y	dec(0,Y+2)
B Y	dec(1,Y+2)

Interpreter

• Common Lisp implementation of the Quests programming language.