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tiddlazy.py
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tiddlazy.py
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#### tiddlyvau.py
#
# Simple Lisp interpreter that uses vau expressions
# to remove all built-in functions and syntactic forms from eval
#
# Adapted from tiddlylisp by Michael Nielsen. See
# http://michaelnielsen.org/ddi/lisp-as-the-maxwells-equations-of-software/
import sys
import traceback
from tiddlyparser import *
class Env(dict):
"An environment: a dict of {'var':val} pairs, with an outer Env."
def __init__(self, bindings={}, outer=None):
self.update(bindings)
self.outer = outer
def __getitem__(self, var):
loc = self.find(var)
val = super(Env,loc).__getitem__(var)
if isa(val, Deferral):
val = eval(val.expr, val.env)
loc[var] = val
return val
def find(self, var):
"Find the innermost Env where var appears."
if var in self:
return self
elif not self.outer is None:
return self.outer.find(var)
else: raise ValueError("%s is not defined"%(var,))
class Deferral():
def __init__(self, expr, env):
self.expr = expr
self.env = env
def define(var,exp):
val = eval(exp)
if not isa(var.expr, Symbol):
raise Exception("Invalid Symbol %s" % (var.expr,))
exp.env[var.expr] = val
return val
def setvar(var, exp):
val = eval(exp)
env.find(var)[var] = val
return val
def quote(exp): return exp.expr
def cond(*x):
for clause in x:
(p, e) = clause.expr
if eval(p,clause.env):
return eval(e,clause.env)
raise ValueError("No Branch Evaluates to True")
def begin(*x):
val = 0
for exp in x:
val = eval(exp)
return val
def vprint(x):
val = eval(x)
print to_string(val)
return val
global_env = Env({
'+': lambda x,y:eval(x)+eval(y),
'-': lambda x,y:eval(x)-eval(y),
'*': lambda x,y:eval(x)*eval(y),
'/': lambda x,y:eval(x)/eval(y),
'>': lambda x,y:eval(x)>eval(y),
'<': lambda x,y:eval(x)<eval(y),
'>=': lambda x,y:eval(x)>=eval(y),
'<=': lambda x,y:eval(x)<=eval(y),
'=': lambda x,y:eval(x)==eval(y),
'eq?': lambda x,y:
(lambda vx,vy: (not isa(vx, list)) and (vx == vy))(eval(x),eval(y)),
'cons': lambda x,y:[eval(x)]+eval(y),
'car': lambda x:eval(x)[0],
'cdr': lambda x:eval(x)[1:],
'list': lambda *x:[eval(exp) for exp in x],
'append': lambda x,y:eval(x)+eval(y),
'len': lambda x:len(eval(x)),
'null?': lambda x:eval(x)==[],
'symbol?': lambda x:isa(eval(x),Symbol),
'list?': lambda x:isa(eval(x),list),
'atom?': lambda x:not isa(eval(x), list),
'exit': lambda:exit(),
'True': True,
'False': False,
'if': lambda test,conseq,alt: eval((conseq if eval(test) else alt)),
'cond': cond,
'define': define,
'set!': setvar,
'lambda': lambda vars, body:
(lambda *args: eval(body.expr, Env(zip(vars.expr, args), body.env))),
'q': quote,
'quote': quote,
'begin': begin,
'print': vprint,
'eval': lambda x,e: eval(x,e)
})
#### eval
def eval(x, env=global_env):
"Evaluate an expression in an environment."
if isa(x, Symbol): # variable reference
return env.find(x)[x]
if isa(x, Deferral):
return eval(x.expr, x.env)
if isa(x, list): # (proc exp*)
proc = eval(x[0], env)
args = [Deferral(expr,env) for expr in x[1:]]
if hasattr(proc, '__call__'): return proc(*args)
else: raise ValueError("%s = %s is not a procedure" % (to_string(x[0]),to_string(proc)))
return x
#### Load from a file and run
def load(filename):
"""
Load the tiddlylisp program in filename, execute it, and start the
repl. If an error occurs, execution stops, and we are left in the
repl. Note that load copes with multi-line tiddlylisp code by
merging lines until the number of opening and closing parentheses
match.
"""
print "Loading and executing %s" % filename
rps = 0
full_line = ""
for line in open(filename, "r"):
line = line.strip()
full_line += line
rps += line.count("(")-line.count(")")
if rps == 0 and full_line.strip() != "":
try:
tokens = tokenize(full_line)
while len(tokens) > 0:
val = eval(parse(tokens))
except SystemExit:
exit()
except:
handle_error()
print "\nThe line in which the error occurred:\n%s" % full_line
break
full_line = ""
#### repl
def repl(prompt='tiddlylisp> '):
"""
A prompt-read-eval-print loop.
"""
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))
if val is not None: print to_string(val)
except (KeyboardInterrupt, SystemExit) as e:
raise e
except ValueError as e:
print e.message
except:
handle_error()
except (KeyboardInterrupt, SystemExit):
print "\nExiting tiddlylisp\n"
except:
print "\nFatal Error\n"
traceback.print_exc()
exit()
#### error handling
def handle_error():
"""
Simple error handling for both the repl and load.
"""
print "An error occurred. Here's the Python stack trace:\n"
traceback.print_exc()
#### on startup from the command line
if __name__ == "__main__":
if len(sys.argv) > 1:
load(sys.argv[1])
repl()
#### on startup from the command line
if __name__ == "__main__":
if len(sys.argv) > 1:
load(sys.argv[1])
repl()