def eval(x, env):
"Evaluate an expression in an environment."
while True:
if isa(x, Symbol): # variable reference
return env[x]
elif isa(x, list): # (proc exp*)
proc = eval(x[0], env)
if hasattr(proc, '__call__'):
val = proc(env,*x[1:])
if isa(val, Tail):
x = val.expr
env = val.env
else:
return val
elif isa(proc, bool): #sugar for boolean branches
x = x[1] if proc else x[2]
else:
raise ValueError("%s = %s is not a procedure" % (to_string(x[0]),to_string(proc)))
else:
return x
def repl(prompt='vernal> '):
try:
while True:
full_line = raw_input(prompt)
rps = full_line.count("(")-full_line.count(")")
while rps != 0 or full_line == "":
line = raw_input(">\t")
full_line += line
rps += line.count("(")-line.count(")")
try:
tokens = tokenize(full_line)
while len(tokens) > 0:
val = eval(parse(tokens),global_env)
if val is not None: print to_string(val)
except ValueError as e:
print e.message
except Exception as e:
raise e
except (KeyboardInterrupt, SystemExit):
pass
except:
print "\nFatal Error\n"
traceback.print_exc()
def vprint(v,e): val = eval(e, v) print to_string(val) return val
