class Interpreter():
"""
A read eval print loop interactive interpreter. Takes input from the user and displays the resultant output on the next line
"""
def __init__(self):
# Windows does not have GNU readline, and has different environment variables
if osname == 'nt':
username = environ["USERNAME"]
else:
import readline
import atexit
username = environ["USER"]
# Uses the readline library to gain tab completion, matching
# parenthesis, and automatic history
readline.set_completer(self.complete)
readline.parse_and_bind('tab: complete')
readline.parse_and_bind('set blink-matching-paren on')
self.histfile = join(expanduser("~"), ".pylisp_history")
try:
readline.read_history_file(self.histfile)
except FileNotFoundError:
open(self.histfile, 'a').close()
self.completion_candidates = []
atexit.register(readline.write_history_file, self.histfile)
# Initialises using the user's username as the prompt
self.prompt = username + "> "
self.intro = "Welcome to the PyLisp interpreter"
self.vm = VirtualMachine({})
self.load_std()
self.registers = None
def load_std(self):
"""
Adds the core libraries to the environment
"""
for i in env.standard_env:
libs = env.include_lib(i)
for lib in libs:
if lib[0] == "py":
self.vm.env.update(lib[1])
elif lib[0] == "pyl":
file_parse = FileParser(lib[1], self.vm)
file_parse.run()
def complete(self, text, state):
"""
The completer function. Works by finding all the symbols in the environment and in the core keywords and checking if they start with the provided text
"""
if state == 0:
self.completion_candidates = []
tmp = []
tmp.extend(self.repl_env.keys())
tmp.extend(self.vm.core_keywords.keys())
for i in tmp:
if i.startswith(text):
self.completion_candidates.append(i)
if state < len(self.completion_candidates):
result = self.completion_candidates[state]
else:
result = None
return result
def precmd(self, line):
"""
Executed on the input before the line is evaluated. Used to ensure that if the opening brackets do not match the closing brackets, the prompt is just extended
"""
ret = line
prompt_indent = len(self.prompt) - len("...")
while ret.count("(") > ret.count(")"):
indent = (ret.count("(") - ret.count(")")) * 2
ret += " " + \
input("\r" + " " * prompt_indent + "..." + indent * " ")
return ret
def cmdloop(self):
"""
The main loop. Gets the input, sends it to precmd, then runs it. If it encounters a pylisp error, prints the error and cleans up.
If it enconters an EOF i.e. Ctrl-D it closes gracefully
"""
print(self.intro)
while True:
self.registers = self.vm.get_registers()
try:
inp = input(self.prompt)
inp = self.precmd(inp)
parser = Parser()
print(self.vm.evaluate(parser.parse_buffer(inp)))
except PylispError as e:
print(e)
self.vm.set_registers(self.registers)
except (KeyboardInterrupt, EOFError):
return
