Lisp Interpreter - Python¶
A personal project to create a Lisp interpreter with Python.
Any suggestions/reviews are welcome.
Contents:
Parser¶
The parser functions and their brief description.
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lispereter.parser.atom(token)¶ Numbers become numbers; every other token is a symbol.
Parameters: token : str
The token to be turned to a LISP atom.
Returns: lisp_atom : Atom
A LISP atom.
Examples
>>> atom("11") 11
>>> atom(11) 11
>>> atom("11.0") 11.0
>>> atom("begin") 'begin'
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lispereter.parser.parse(program)¶ Read a Scheme expression from a string.
Parameters: program : str
The expression to parse.
Returns: expression : Exp
A Scheme expression (list/atom).
Examples
>>> parse("(begin (define r 10) (* pi (* r r)))") ['begin', ['define', 'r', 10], ['*', 'pi', ['*', 'r', 'r']]]
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lispereter.parser.read_from_tokens(tokens)¶ Read an expression from a sequence of tokens.
Parameters: tokens : list
A list of tokens.
Returns: parsable : Exp
An expression to be parsed.
Examples
>>> read_from_tokens(['(', 'begin', '(', 'define', 'r', '10', ')', '(', '*', 'pi', '(', '*', 'r', 'r', ')', ')', ')']) ['begin', ['define', 'r', 10], ['*', 'pi', ['*', 'r', 'r']]]
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lispereter.parser.tokenize(chars)¶ Convert a string of characters into a list of tokens.
Parameters: chars : str
The input string to tokenize.
Returns: token_list : List
A list of tokens.
Examples
>>> tokenize("(begin (define r 10) (* pi (* r r)))") ['(', 'begin', '(', 'define', 'r', '10', ')', '(', '*', 'pi', '(', '*', 'r', 'r', ')', ')', ')']
Eval¶
The evaluate function, and Env and Procedure class.
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class
lispereter.environ.Env(params=(), args=(), outer=None)¶ An environment: a dict of {‘var’: val} paris, with an outer Env.
Parameters: params : set, optional
Set of variables.
args : set, optional
The values associated with variables in params.
outer : Env, optional
Outer environment
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find(var)¶ Find the innermost environment where the variable occurs.
Parameters: var : str
The variable to find.
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class
lispereter.environ.Procedure(params, body, env)¶ A user-defined Scheme procedure.
Parameters: params : set
A set of parameters for the procedure.
body : str
The actual expression of the procedure to execute.
env : Env
The current environment of the procedure.
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lispereter.environ.evaluate(x, env=global_env)¶ Evaluate a given expression x using env.
Parameters: x : Exp
The expression to evaluate.
env : dict, optional
The environment holding the variables etc.
Returns: val : (Exp, Atom)
Some answer.
Examples
>>> evaluate(parse("(begin (define r 10) (* pi (* r r)))")) 314.1592653589793
>>> evaluate(parse('(if (< 2 3) (print 2) (print 3))')) 2