def tostring(a):
if islist(a):
return '(' + ' '.join(map(str, a)) + ')'
elif isbool(a):
return '#t' if a else '#f'
else:
return str(a)
def tostring(a):
if islist(a):
return '(' + ' '.join(map(str, a)) + ')'
elif isbool(a):
return '#t' if a else '#f'
else:
return str(a)
def eval(sexp, env):
if islist(sexp):
op = sexp[0]
if op == 'begin':
for exp in sexp[1:-1]:
eval(exp, env)
return eval(sexp[-1], env)
elif op == 'quote':
return sexp[1]
elif op == 'lambda':
exps = sexp[2:]
exps.insert(0, 'begin')
return Lambda(env, sexp[1], exps)
elif op == 'cond':
for cond_exp in sexp[1:]:
cond = cond_exp[0]
exp = cond_exp[1:]
if eval(cond, env):
exp.insert(0, 'begin')
return eval(exp, env)
elif op == 'define':
defn = eval(sexp[2], env)
env.update({sexp[1]: defn})
return defn
elif op == 'and':
for exp in sexp[1:]:
if not eval(exp, env):
return False
return True
elif op == 'or':
for exp in sexp[1:]:
if eval(exp, env):
return True
return False
else: # apply
op = eval(sexp[0], env)
args = []
for exp in sexp[1:]:
args.append(eval(exp, env))
return op(*args)
elif sexp == '#t':
return True
elif sexp == '#f':
return False
elif isnumber(sexp):
return sexp
else:
return env.find(sexp)
def eval(sexp, env):
if islist(sexp):
op = sexp[0]
if op == 'begin':
for exp in sexp[1:-1]:
eval(exp, env)
return eval(sexp[-1], env)
elif op == 'quote':
return sexp[1]
elif op == 'lambda':
exps = sexp[2:]
exps.insert(0, 'begin')
return Lambda(env, sexp[1], exps)
elif op == 'cond':
for cond_exp in sexp[1:]:
cond = cond_exp[0]
exp = cond_exp[1:]
if eval(cond, env):
exp.insert(0, 'begin')
return eval(exp, env)
elif op == 'define':
defn = eval(sexp[2], env)
env.update({sexp[1]: defn})
return defn
elif op == 'and':
for exp in sexp[1:]:
if not eval(exp, env):
return False
return True
elif op == 'or':
for exp in sexp[1:]:
if eval(exp, env):
return True
return False
else: # apply
op = eval(sexp[0], env)
args = []
for exp in sexp[1:]:
args.append(eval(exp, env))
return op(*args)
elif sexp == '#t':
return True
elif sexp == '#f':
return False
elif isnumber(sexp):
return sexp
else:
return env.find(sexp)
