def cond(args, env):
l = list(args)
for i, s in enumerate(l):
if s.car == Symbol('else') or scheme_eval(s.car, env) != Symbol('#f'):
if s.car == Symbol('else') and i != len(l) - 1:
raise SyntaxError('Misplaced ELSE clause')
return scheme_eval(Cell(Symbol('begin'), s.cdr), env)
def let_star(args, env):
if args.car.null:
return scheme_eval(Cell(Symbol('begin'), args.cdr), env)
else:
return let_star(Cell(args.car.cdr, args.cdr),
Environment(env,
{args.car.car.car:
scheme_eval(args.car.car.cdr.car, env)}))
def let(args, env):
var_list = args.car
body = args.cdr
argnames = cons_list(i.car for i in var_list)
arg_values = cons_list(scheme_eval(i.cdr.car, env) for i in var_list)
l = create_lambda(Cell(argnames, body), env)
return l(arg_values)
def define(args, env):
if type(args.car) is Symbol:
env.define(args.car, scheme_eval(args.cdr.car, env))
elif type(args.car) is Cell:
name = args.car.car
arguments = args.car.cdr
body = args.cdr
if arguments.car == Symbol('.'):
arguments = arguments.cdr.car
env.define(name, create_lambda(Cell(arguments, body), env))
def repl():
code = ''
while True:
code += input()
try:
parsed = parse(code)
except SyntaxError as e:
code += '\n'
continue
else:
result = scheme_eval(parsed, global_env)
print(result if result is not None else 'Unspecified value')
code = ''
def file_eval(filename):
with open(filename, 'r') as program_file:
code = program_file.read()
code = '(begin ' + code + ')'
parsed = parse(code)
scheme_eval(parsed, global_env)
def scheme_apply(args, env):
return scheme_eval(Cell(args.car, scheme_eval(args.cdr.car, env)), env)
def scheme_or(args, env):
for i in iter(args):
result = scheme_eval(i, env)
if result != scheme_false:
return result
return scheme_false
