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# This module tries to implement ISO 14977 standard with pyparsing.
# pyparsing version 1.1 or greater is required.
# ISO 14977 standardize The Extended Backus-Naur Form(EBNF) syntax.
# You can read a final draft version here:
# https://www.cl.cam.ac.uk/~mgk25/iso-ebnf.html
#
# Submitted 2004 by Seo Sanghyeon
#
from pyparsing import *
all_names = """
integer
meta_identifier
terminal_string
optional_sequence
repeated_sequence
grouped_sequence
syntactic_primary
syntactic_factor
syntactic_term
single_definition
definitions_list
syntax_rule
syntax
""".split()
integer = Word(nums)
meta_identifier = Word(alphas, alphanums + "_")
terminal_string = Suppress("'") + CharsNotIn("'") + Suppress("'") ^ Suppress(
'"'
) + CharsNotIn('"') + Suppress('"')
definitions_list = Forward()
optional_sequence = Suppress("[") + definitions_list + Suppress("]")
repeated_sequence = Suppress("{") + definitions_list + Suppress("}")
grouped_sequence = Suppress("(") + definitions_list + Suppress(")")
syntactic_primary = (
optional_sequence
^ repeated_sequence
^ grouped_sequence
^ meta_identifier
^ terminal_string
)
syntactic_factor = Optional(integer + Suppress("*")) + syntactic_primary
syntactic_term = syntactic_factor + Optional(Suppress("-") + syntactic_factor)
single_definition = delimitedList(syntactic_term, ",")
definitions_list << delimitedList(single_definition, "|")
syntax_rule = meta_identifier + Suppress("=") + definitions_list + Suppress(";")
ebnfComment = (
("(*" + ZeroOrMore(CharsNotIn("*") | ("*" + ~Literal(")"))) + "*)")
.streamline()
.setName("ebnfComment")
)
syntax = OneOrMore(syntax_rule)
syntax.ignore(ebnfComment)
def do_integer(str, loc, toks):
return int(toks[0])
def do_meta_identifier(str, loc, toks):
if toks[0] in symbol_table:
return symbol_table[toks[0]]
else:
forward_count.value += 1
symbol_table[toks[0]] = Forward()
return symbol_table[toks[0]]
def do_terminal_string(str, loc, toks):
return Literal(toks[0])
def do_optional_sequence(str, loc, toks):
return Optional(toks[0])
def do_repeated_sequence(str, loc, toks):
return ZeroOrMore(toks[0])
def do_grouped_sequence(str, loc, toks):
return Group(toks[0])
def do_syntactic_primary(str, loc, toks):
return toks[0]
def do_syntactic_factor(str, loc, toks):
if len(toks) == 2:
# integer * syntactic_primary
return And([toks[1]] * toks[0])
else:
# syntactic_primary
return [toks[0]]
def do_syntactic_term(str, loc, toks):
if len(toks) == 2:
# syntactic_factor - syntactic_factor
return NotAny(toks[1]) + toks[0]
else:
# syntactic_factor
return [toks[0]]
def do_single_definition(str, loc, toks):
toks = toks.asList()
if len(toks) > 1:
# syntactic_term , syntactic_term , ...
return And(toks)
else:
# syntactic_term
return [toks[0]]
def do_definitions_list(str, loc, toks):
toks = toks.asList()
if len(toks) > 1:
# single_definition | single_definition | ...
return Or(toks)
else:
# single_definition
return [toks[0]]
def do_syntax_rule(str, loc, toks):
# meta_identifier = definitions_list ;
assert toks[0].expr is None, "Duplicate definition"
forward_count.value -= 1
toks[0] << toks[1]
return [toks[0]]
def do_syntax(str, loc, toks):
# syntax_rule syntax_rule ...
return symbol_table
symbol_table = {}
class forward_count:
pass
forward_count.value = 0
for name in all_names:
expr = vars()[name]
action = vars()["do_" + name]
expr.setName(name)
expr.setParseAction(action)
# ~ expr.setDebug()
def parse(ebnf, given_table={}):
symbol_table.clear()
symbol_table.update(given_table)
forward_count.value = 0
table = syntax.parseString(ebnf)[0]
assert forward_count.value == 0, "Missing definition"
for name in table:
expr = table[name]
expr.setName(name)
# ~ expr.setDebug()
return table