Divrac

Divrac is an OISC by User:PythonshellDebugwindow.

Memory

Divrac uses an unbounded number of memory slots, each of which can hold a signed integer. All slots are assigned a index, which is a nonnegative integer.

Syntax

A program is made up of zero or more lines. Each line is of the form:

a,b,c,d,n

with optional (ignored) vertical whitespace. Lines are separated by newlines.

$a$, $b$, $c$, $d$, and $n$ must be either integers, representing integer values, or integers surrounded by any number of brackets. Each pair of brackets represents a level of indirection. For example, 1 represents the number 1, [1] represents the value in the 1st memory space, [[1]] represents the value in the $m$th memory space where $m$ is the value in the 1st memory slot, and so on.

BNF

Remove all vertical whitespace first.

program ::= lines | line | ""
lines ::= line "\n" | lines lines
line ::= val "," val "," val "," val "," val
val ::= int | "[" val "]"
int ::= digit | digit int

Semantics

Each line, the numerator and denominator of the reduced improper form of ${\frac {a}{b}}\div {\frac {c}{d}}$ are calculated. If $n$ is nonnegative, the numerator is stored in the $n$th memory slot, and the denominator in the $n+1$th.

If, however, $n$ is negative, then it prints the numerator to STDOUT if it is -2, and sets the instruction pointer to the numerator if it is -1 (any other value is undefined behaviour).

A negative value of $a$, $b$, $c$, or $d$ represents a special value: $-1$ represents the value of the instruction pointer, $-2$ reads a positive integer from STDIN, and all other negative values of these four are undefined behaviour.

Division by zero at any point causes the program to exit. If the numerator of ${\frac {a}{b}}\div {\frac {c}{d}}$ is 0, then the denominator is redefined to be a random integer from 1 to 1000.

Examples

Truth-machine

Using the I/O extension:

0,1,1,1,0
1,1,1,1,1
[-2],1,1,1,2
[2],1,1,1,-2
1,1,[2],1,3
4,1,1,1,-1

Implementations

Swift

See #External resources.

Python 3

It is not specified what should happen if $n<-2$. This implementation treats it as a nop. It also assumes that setting the IP to an invalid line number is a valid way to halt a program.

   import sys
   from math import gcd
   from functools import partial
   from collections import defaultdict
   def process(ip,entry,special=False):
       global memory
       if isinstance(entry,list):
           if len(entry)!=1: print("Invalid entry on line %d: %s"%(ip,str(entry)));sys.exit(1)
           return memory[process(ip,entry[0],special=special)]
       elif type(entry) == int:
           if special:
               return entry
           else:
               if entry>=0:
                   return entry
               elif entry==-1:
                   return ip+1
               elif entry==-2:
                   return int(input())
               else:
                   print("Invalid entry on line %d: %d"%(ip,entry));sys.exit(1)
       else:
           print("Invalid entry on line %d: %s"%(ip,str(entry)));sys.exit(1)
   if len(sys.argv)<2:
       print("No filename to execute.")
   else:
       try: 
           with open(sys.argv[1], "r") as f:
               prog = f.read().splitlines()
       except IOError: print("File '"+filename+"' not found."); sys.exit(1)
       for i in range(len(prog)):
           line = prog[i].strip()
           if not line: i-=1;continue
           try:
               prog[i] = list(map(eval,line.split(",")))
           except: print("Invalid instruction on line %d"%(i)); sys.exit(1)
       memory = defaultdict(int)
       ip = 0
       while 0<=ip<len(prog):
           line = prog[ip]
           a,b,c,d = map(partial(process,ip),line[:4])
           n=process(ip,line[4],special=True)
           numer = a*d
           denom = b*c
           if denom==0:sys.exit(1)
           div = gcd(numer,denom)
           numer//=div
           denom//=div
           if n>=0:
               memory[n]=numer
               memory[n+1]=denom
           elif n==-1:
               ip=numer-2
           elif n==-2:
               print(numer)
           ip+=1

External resources

• Divrac.swift on GitHub