Parser is WIP
need to debug _parse_expression
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Eli Bendersky
parent
33cfaccf9e
commit
37b239ee0d
2 changed files with 289 additions and 106 deletions
289
chapter2.py
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289
chapter2.py
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@ -0,0 +1,289 @@
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# Chapter 1 - Lexer
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from collections import namedtuple
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from enum import Enum
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# Each token is a tuple of kind and value. kind is one of the enumeration values
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# in TokenKind. value is the textual value of the token in the input.
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class TokenKind(Enum):
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EOF = -1
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DEF = -2
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EXTERN = -3
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IDENTIFIER = -4
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NUMBER = -5
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OPERATOR = -6
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Token = namedtuple('Token', 'kind value')
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class Lexer(object):
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"""Lexer for Kaleidoscope.
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Initialize the lexer with a string buffer. tokens() returns a generator that
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can be queried for tokens. The generator will emit an EOF token before
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stopping.
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"""
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def __init__(self, buf):
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assert len(buf) >= 1
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self.buf = buf
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self.pos = 0
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self.lastchar = self.buf[0]
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def tokens(self):
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while self.lastchar:
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# Skip whitespace
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while self.lastchar.isspace():
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self._advance()
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# Identifier or keyword
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if self.lastchar.isalpha():
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id_str = ''
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while self.lastchar.isalnum():
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id_str += self.lastchar
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self._advance()
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if id_str == 'def':
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yield Token(kind=TokenKind.DEF, value=id_str)
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elif id_str == 'extern':
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yield Token(kind=TokenKind.EXTERN, value=id_str)
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else:
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yield Token(kind=TokenKind.IDENTIFIER, value=id_str)
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# Number
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elif self.lastchar.isdigit() or self.lastchar == '.':
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num_str = ''
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while self.lastchar.isdigit() or self.lastchar == '.':
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num_str += self.lastchar
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self._advance()
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yield Token(kind=TokenKind.NUMBER, value=num_str)
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# Comment
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elif self.lastchar == '#':
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self._advance()
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while self.lastchar and self.lastchar not in '\r\n':
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self._advance()
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elif self.lastchar:
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# Some other char
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yield Token(kind=TokenKind.OPERATOR, value=self.lastchar)
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self._advance()
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yield Token(kind=TokenKind.EOF, value='')
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def _advance(self):
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try:
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self.pos += 1
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self.lastchar = self.buf[self.pos]
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except IndexError:
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self.lastchar = ''
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# AST hierarchy
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class ASTNode(object):
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pass
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class ExprAST(ASTNode):
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pass
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class NumberExprAST(ExprAST):
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def __init__(self, val):
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self.val = val
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class VariableExprAST(ExprAST):
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def __init__(self, name):
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self.name = name
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class BinaryExprAST(ExprAST):
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def __init__(self, op, lhs, rhs):
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self.op = op
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self.lhs = lhs
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self.rhs = rhs
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class CallExprAST(ExprAST):
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def __init__(self, callee, args):
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self.callee = callee
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self.args = args
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class PrototypeAST(ASTNode):
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def __init__(self, name, args):
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self.name = name
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self.args = args
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class FunctionAST(ASTNode):
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def __init__(self, proto, body):
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self.proto = proto
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self.body = body
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class ParseError(Exception): pass
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class Parser(object):
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def __init__(self, buf):
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self.token_generator = Lexer(buf).tokens()
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self.cur_tok = None
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self._get_next_token()
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def _get_next_token(self):
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self.cur_tok = next(self.token_generator)
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_precedence_map = {'<': 10, '+': 20, '-': 20, '*': 40}
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def _cur_tok_precedence(self):
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"""Get the operator precedence of the current token."""
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try:
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return Parser._precedence_map[self.cur_tok]
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except KeyError:
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return -1
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def _cur_tok_is_operator(self, op):
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"""Query whether the current token is the operator 'op'"""
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return (self.cur_tok.kind == TokenKind.OPERATOR and
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self.cur_tok.value == 'op')
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# identifierexpr
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# ::= identifier
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# ::= identifier '(' expression* ')'
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def _parse_identifier_expr(self):
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id_name = self.cur_tok.value
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self._get_next_token()
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# If followed by a '(' it's a call; otherwise, a simple variable ref.
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if self._cur_tok_is_operator('('):
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return VariableExprAST(id_name)
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self._get_next_token()
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args = []
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if not self._cur_tok_is_operator(')'):
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while True:
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args.push_back(self._parse_expression())
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if self._cur_tok_is_operator(')'):
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break
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if not self._cur_tok_is_operator(','):
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raise ParseError('Expected ")" or "," in argument list')
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self._get_next_token()
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self._get_next_token() # consume the ')'
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return CallExprAST(id_name, args)
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# numberexpr ::= number
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def _parse_number_expr(self):
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result = NumberExprAST(self.cur_tok.value)
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self._get_next_token() # consume the number
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return result
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# parenexpr ::= '(' expression ')'
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def _parse_paren_expr(self):
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self._get_next_token() # consume the '('
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expr = self._parse_expression()
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if not self._cur_tok_is_operator(')'):
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raise ParseError('Expected ")"')
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self._get_next_token() # consume the ')'
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return expr
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# primary
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# ::= identifierexpr
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# ::= numberexpr
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# ::= parenexpr
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def _parse_primary(self):
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if self.cur_tok.kind == TokenKind.IDENTIFIER:
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return self._parse_identifier_expr()
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elif self.cur_tok.kind == TokenKind.NUMBER:
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return self._parse_number_expr()
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elif self._cur_tok_is_operator('('):
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return self._parse_paren_expr()
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else:
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raise ParseError('Unknown token when expecting an expression')
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# binoprhs ::= (<binop> primary)*
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def _parse_binop_rhs(self, expr_prec, lhs_ast):
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"""Parse the right-hand-side of a binary expression.
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expr_prec: minimal precedence to keep going (precedence climbing).
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lhs_ast: AST of the left-hand-side.
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"""
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while True:
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cur_prec = self._cur_tok_precedence()
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# If this is a binary operator with precedence lower than the
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# currently parsed sub-expression, bail out. If it binds at least
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# as tightly, keep going.
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# Note that the precedence of non-operators is defined to be -1,
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# so this condition handles cases when the expression ended.
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if cur_prec < expr_prec:
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return lhs_ast
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op = self.cur_tok.value
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self._get_next_token() # consume the operator
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rhs = self._parse_primary()
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next_prec = self._cur_tok_precedence()
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# There are three options:
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# 1. next_prec > cur_prec: we need to make a recursive call
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# 2. next_prec == cur_prec: no need for a recursive call, the next
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# iteration of this loop will handle it.
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# 3. next_prec < cur_prec: no need for a recursive call, combine
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# lhs and the next iteration will immediately bail out.
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if cur_prec < next_prec:
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rhs = self._parse_binop_rhs(cur_prec + 1, rhs)
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# Merge lhs/rhs
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lhs = BinaryExprAST(op, lhs, rhs)
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# expression ::= primary binoprhs
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def _parse_expression(self):
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lhs = self._parse_primary()
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# Start with precedence 0 because we want to bind any operator to the
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# expression at this point.
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return self._parse_binop_rhs(0, lhs)
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#---- Some unit tests ----#
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import unittest
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class TestLexer(unittest.TestCase):
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def _assert_toks(self, toks, kinds):
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"""Assert that the list of toks has the given kinds."""
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self.assertEqual([t.kind.name for t in toks], kinds)
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def test_lexer_simple_tokens_and_values(self):
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l = Lexer('a+1')
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toks = list(l.tokens())
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self.assertEqual(toks[0], Token(TokenKind.IDENTIFIER, 'a'))
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self.assertEqual(toks[1], Token(TokenKind.OPERATOR, '+'))
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self.assertEqual(toks[2], Token(TokenKind.NUMBER, '1'))
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self.assertEqual(toks[3], Token(TokenKind.EOF, ''))
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l = Lexer('.1519')
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toks = list(l.tokens())
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self.assertEqual(toks[0], Token(TokenKind.NUMBER, '.1519'))
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def test_token_kinds(self):
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l = Lexer('10.1 def der extern foo (')
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self._assert_toks(
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list(l.tokens()),
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['NUMBER', 'DEF', 'IDENTIFIER', 'EXTERN', 'IDENTIFIER',
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'OPERATOR', 'EOF'])
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l = Lexer('+- 1 2 22 22.4 a b2 C3d')
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self._assert_toks(
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list(l.tokens()),
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['OPERATOR', 'OPERATOR', 'NUMBER', 'NUMBER', 'NUMBER', 'NUMBER',
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'IDENTIFIER', 'IDENTIFIER', 'IDENTIFIER', 'EOF'])
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def test_skip_whitespace_comments(self):
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l = Lexer('''
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def foo # this is a comment
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# another comment
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\t\t\t10
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''')
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self._assert_toks(
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list(l.tokens()),
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['DEF', 'IDENTIFIER', 'NUMBER', 'EOF'])
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if __name__ == '__main__':
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buf = '''2+3'''
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p = Parser(buf)
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print(p._parse_expression())
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106
part1.py
106
part1.py
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@ -1,106 +0,0 @@
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# Chapter 1 - Lexer
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from collections import namedtuple
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from enum import Enum
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# Each token is a tuple of kind and value. kind is one of the enumeration values
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# in TokenKind. value is the textual value of the token in the input.
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class TokenKind(Enum):
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EOF = -1
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DEF = -2
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EXTERN = -3
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IDENTIFIER = -4
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NUMBER = -5
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OPERATOR = -6
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Token = namedtuple('Token', 'kind value')
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class Lexer(object):
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"""Lexer for Kaleidoscope.
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Initialize the lexer with a string buffer. tokens() returns a generator that
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can be queried for tokens. The generator will emit an EOF token before
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stopping.
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"""
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def __init__(self, buf):
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assert len(buf) >= 1
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self.buf = buf
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self.pos = 0
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self.lastchar = self.buf[0]
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def tokens(self):
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while self.lastchar:
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# Skip whitespace
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while self.lastchar.isspace():
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self._advance()
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# Identifier or keyword
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if self.lastchar.isalpha():
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id_str = ''
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while self.lastchar.isalnum():
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id_str += self.lastchar
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self._advance()
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if id_str == 'def':
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yield Token(kind=TokenKind.DEF, value=id_str)
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elif id_str == 'extern':
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yield Token(kind=TokenKind.EXTERN, value=id_str)
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else:
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yield Token(kind=TokenKind.IDENTIFIER, value=id_str)
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# Number
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elif self.lastchar.isdigit() or self.lastchar == '.':
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num_str = ''
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while self.lastchar.isdigit() or self.lastchar == '.':
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num_str += self.lastchar
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self._advance()
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yield Token(kind=TokenKind.NUMBER, value=num_str)
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# Comment
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elif self.lastchar == '#':
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self._advance()
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while self.lastchar and self.lastchar not in '\r\n':
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self._advance()
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else:
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# Some other char
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yield Token(kind=TokenKind.OPERATOR, value=self.lastchar)
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self._advance()
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yield Token(kind=TokenKind.EOF, value='')
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def _advance(self):
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try:
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self.pos += 1
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self.lastchar = self.buf[self.pos]
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except IndexError:
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self.lastchar = ''
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import unittest
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class TestLexer(unittest.TestCase):
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def test_lexer_simpletokens(self):
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l = Lexer('a+b(koko*.12+115)')
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toks = list(l.tokens())
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self.assertEqual(toks[0].kind, TokenKind.IDENTIFIER)
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if __name__ == '__main__':
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buf = '''
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# Compute the x'th fibonacci number.
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def fib(x)
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if x < 3 then
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1
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else
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fib(x-1)+fib(x-2)
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# This expression will compute the 40th number.
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fib(40)
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'''
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l = Lexer(buf)
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tokengen = l.tokens()
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#for i in range(4):
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#print(next(tokengen))
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#print(list(tokengen))
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for t in tokengen:
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print(t)
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