fn.py

import pyparsing as pp
from pyparsing import pyparsing_common as ppc

from repl import repl


class Node:
    def __init__(self, name, *args):
        self.name = name
        self.items = args

    def __repr__(self):
        return '{}({})'.format(self.name, ', '.join(repr(i) for i in self.items))


string = pp.quotedString.copy()
string.setParseAction(lambda t: t[0][1:-1])
atom = ppc.integer ^ ppc.fnumber | string
node = pp.Forward()
node <<= ppc.identifier + pp.Suppress('(') + pp.Optional(pp.delimitedList(atom | node)) + pp.Suppress(')')
node.setParseAction(lambda t: Node(*t))
repl(node)

repl.py

from prompt_toolkit import prompt
from prompt_toolkit.history import InMemoryHistory
from pyparsing import ParseBaseException


def sgr(*args):
    return '\x1b[{}m'.format(';'.join(str(i) for i in args))


def repl(parser):
    parser.validate()
    history = InMemoryHistory()
    while True:
        try:
            s = prompt('> ', history=history)
            result = parser.parseString(s, parseAll=True)
            for item in result:
                print(item)
        except ParseBaseException as err:
            print(f'{sgr(1, 31)}{err.__class__.__name__}{sgr(0)}: {err}')
        except KeyboardInterrupt:
            pass
        except EOFError:
            break