Write a ~ATH Interpreter
Python 2.7.6, 1244 1308 1265 1253 1073 1072 1071 1065 1064 1063 bytes
Alright, I'm not breaking any records here but this is about the smallest Python will go insofar as reading input all at once from a file rather than sequentially over time. I'll try to one-up this later in a different language (and an interpreter, not just a parser). Until then, enjoy the disgustingly horrid monstrosity.
Note: opens a file called t in the working directory. To make it open a command line argument, add import sys to the top of the file and change 't' to sys.argv[1]

n=s='\n';m=',';X='[';Y=']';c=';';A='~ATH';D='import';b,g,k=[],[],[];r=range;l=len;f=open('t','r').read().split(n)
def d(j,u):
 p=[]
 for e in j:
  if e!=u:p.append(e)
 return''.join(p)
for h in r(l(f)):f[h]=f[h].split('//')[0].split()
while[]in f:f.remove([])
for h in r(l(f)):
 i=f[h]
 if i[0]==D and l(i)==2and i[1][l(i[1])-1]==c and d(i[1],c)not in b:g.append(0);b.append(d(i[1],c))
 elif i[0].startswith(A):
  i=i[0].split('){')
  for e in r(l(i)):
   if i[e].startswith(A):
    i[e]=i[e].split('(')
    if i[0][1]in b:g[b.index(i[0][1])]+=(i[1].count('+')-i[1].count('-'))
 elif i[0].startswith('bifurcate')and l(i)==2and i[1][l(i[1])-1]==c:
  i=i[1].split(X)
  if i[0] in b:
   z=d(d(i[1],c),Y).split(m)
   for e in r(l(z)):g.append(g[b.index(i[0])]);b.append(z[e])
   g.remove(g[b.index(i[0])]);b.remove(i[0])
 elif i[0].startswith(X)and i[0].endswith('.DIE();')and l(i)==1:
  z=d(i[0],X).split(Y)[0].split(m)
  for e in r(l(z)):
   k.append((z[e],g[b.index(z[e])]))
for e in r(l(k)):k0=k[e][0];k1=k[e][1];s+=k0+'='+str(k1)+n+('DIE '+k0+n)*abs(k1)
print s