--- /dev/null
+# GardenSnake - a parser generator demonstration program
+#
+# This implements a modified version of a subset of Python:
+# - only 'def', 'return' and 'if' statements
+# - 'if' only has 'then' clause (no elif nor else)
+# - single-quoted strings only, content in raw format
+# - numbers are decimal.Decimal instances (not integers or floats)
+# - no print statment; use the built-in 'print' function
+# - only < > == + - / * implemented (and unary + -)
+# - assignment and tuple assignment work
+# - no generators of any sort
+# - no ... well, no quite a lot
+
+# Why? I'm thinking about a new indentation-based configuration
+# language for a project and wanted to figure out how to do it. Once
+# I got that working I needed a way to test it out. My original AST
+# was dumb so I decided to target Python's AST and compile it into
+# Python code. Plus, it's pretty cool that it only took a day or so
+# from sitting down with Ply to having working code.
+
+# This uses David Beazley's Ply from http://www.dabeaz.com/ply/
+
+# This work is hereby released into the Public Domain. To view a copy of
+# the public domain dedication, visit
+# http://creativecommons.org/licenses/publicdomain/ or send a letter to
+# Creative Commons, 543 Howard Street, 5th Floor, San Francisco,
+# California, 94105, USA.
+#
+# Portions of this work are derived from Python's Grammar definition
+# and may be covered under the Python copyright and license
+#
+# Andrew Dalke / Dalke Scientific Software, LLC
+# 30 August 2006 / Cape Town, South Africa
+
+# Changelog:
+# 30 August - added link to CC license; removed the "swapcase" encoding
+
+# Modifications for inclusion in PLY distribution
+import sys
+from pprint import pprint
+from copy import copy
+from ply import *
+
+##### Lexer ######
+#import lex
+import decimal
+
+tokens = (
+ 'DEF',
+ 'IF',
+ 'NAME',
+ 'NUMBER', # Python decimals
+ 'STRING', # single quoted strings only; syntax of raw strings
+ 'LPAR',
+ 'RPAR',
+ 'COLON',
+ 'EQ',
+ 'ASSIGN',
+ 'LT',
+ 'GT',
+ 'PLUS',
+ 'MINUS',
+ 'MULT',
+ 'DIV',
+ 'RETURN',
+ 'WS',
+ 'NEWLINE',
+ 'COMMA',
+ 'SEMICOLON',
+ 'INDENT',
+ 'DEDENT',
+ 'ENDMARKER',
+ )
+
+#t_NUMBER = r'\d+'
+# taken from decmial.py but without the leading sign
+def t_NUMBER(t):
+ r"""(\d+(\.\d*)?|\.\d+)([eE][-+]? \d+)?"""
+ t.value = decimal.Decimal(t.value)
+ return t
+
+def t_STRING(t):
+ r"'([^\\']+|\\'|\\\\)*'" # I think this is right ...
+ t.value=t.value[1:-1].decode("string-escape") # .swapcase() # for fun
+ return t
+
+t_COLON = r':'
+t_EQ = r'=='
+t_ASSIGN = r'='
+t_LT = r'<'
+t_GT = r'>'
+t_PLUS = r'\+'
+t_MINUS = r'-'
+t_MULT = r'\*'
+t_DIV = r'/'
+t_COMMA = r','
+t_SEMICOLON = r';'
+
+# Ply nicely documented how to do this.
+
+RESERVED = {
+ "def": "DEF",
+ "if": "IF",
+ "return": "RETURN",
+ }
+
+def t_NAME(t):
+ r'[a-zA-Z_][a-zA-Z0-9_]*'
+ t.type = RESERVED.get(t.value, "NAME")
+ return t
+
+# Putting this before t_WS let it consume lines with only comments in
+# them so the latter code never sees the WS part. Not consuming the
+# newline. Needed for "if 1: #comment"
+def t_comment(t):
+ r"[ ]*\043[^\n]*" # \043 is '#'
+ pass
+
+
+# Whitespace
+def t_WS(t):
+ r'[ ]+'
+ if t.lexer.at_line_start and t.lexer.paren_count == 0:
+ return t
+
+# Don't generate newline tokens when inside of parenthesis, eg
+# a = (1,
+# 2, 3)
+def t_newline(t):
+ r'\n+'
+ t.lexer.lineno += len(t.value)
+ t.type = "NEWLINE"
+ if t.lexer.paren_count == 0:
+ return t
+
+def t_LPAR(t):
+ r'\('
+ t.lexer.paren_count += 1
+ return t
+
+def t_RPAR(t):
+ r'\)'
+ # check for underflow? should be the job of the parser
+ t.lexer.paren_count -= 1
+ return t
+
+#t_ignore = " "
+
+def t_error(t):
+ raise SyntaxError("Unknown symbol %r" % (t.value[0],))
+ print ("Skipping", repr(t.value[0]))
+ t.lexer.skip(1)
+
+## I implemented INDENT / DEDENT generation as a post-processing filter
+
+# The original lex token stream contains WS and NEWLINE characters.
+# WS will only occur before any other tokens on a line.
+
+# I have three filters. One tags tokens by adding two attributes.
+# "must_indent" is True if the token must be indented from the
+# previous code. The other is "at_line_start" which is True for WS
+# and the first non-WS/non-NEWLINE on a line. It flags the check so
+# see if the new line has changed indication level.
+
+# Python's syntax has three INDENT states
+# 0) no colon hence no need to indent
+# 1) "if 1: go()" - simple statements have a COLON but no need for an indent
+# 2) "if 1:\n go()" - complex statements have a COLON NEWLINE and must indent
+NO_INDENT = 0
+MAY_INDENT = 1
+MUST_INDENT = 2
+
+# only care about whitespace at the start of a line
+def track_tokens_filter(lexer, tokens):
+ oldignore = lexer.lexignore
+ lexer.at_line_start = at_line_start = True
+ indent = NO_INDENT
+ saw_colon = False
+ for token in tokens:
+ #print ("token", token)
+ token.at_line_start = at_line_start
+
+ if token.type == "COLON":
+ at_line_start = False
+ indent = MAY_INDENT
+ token.must_indent = False
+
+ elif token.type == "NEWLINE":
+ at_line_start = True
+ if indent == MAY_INDENT:
+ indent = MUST_INDENT
+ token.must_indent = False
+
+ elif token.type == "WS":
+ assert token.at_line_start == True
+ at_line_start = True
+ token.must_indent = False
+
+ else:
+ # A real token; only indent after COLON NEWLINE
+ if indent == MUST_INDENT:
+ token.must_indent = True
+ else:
+ token.must_indent = False
+ at_line_start = False
+ indent = NO_INDENT
+
+ # really bad hack that changes ignore lexer state.
+ # when "must indent" is seen (basically "real tokens" seen)
+ # then ignore whitespace.
+ if token.must_indent:
+ lexer.lexignore = ('ignore', ' ')
+ else:
+ lexer.lexignore = oldignore
+
+ token.indent = indent
+ yield token
+ lexer.at_line_start = at_line_start
+
+def _new_token(type, lineno):
+ tok = lex.LexToken()
+ tok.type = type
+ tok.value = None
+ tok.lineno = lineno
+ tok.lexpos = -1
+ return tok
+
+# Synthesize a DEDENT tag
+def DEDENT(lineno):
+ return _new_token("DEDENT", lineno)
+
+# Synthesize an INDENT tag
+def INDENT(lineno):
+ return _new_token("INDENT", lineno)
+
+
+# Track the indentation level and emit the right INDENT / DEDENT events.
+def indentation_filter(tokens):
+ # A stack of indentation levels; will never pop item 0
+ levels = [0]
+ token = None
+ depth = 0
+ prev_was_ws = False
+ for token in tokens:
+ if 1:
+ print "Process", depth, token.indent, token,
+ if token.at_line_start:
+ print "at_line_start",
+ if token.must_indent:
+ print "must_indent",
+ print
+
+ # WS only occurs at the start of the line
+ # There may be WS followed by NEWLINE so
+ # only track the depth here. Don't indent/dedent
+ # until there's something real.
+ if token.type == "WS":
+ assert depth == 0
+ depth = len(token.value)
+ prev_was_ws = True
+ # WS tokens are never passed to the parser
+ continue
+
+ if token.type == "NEWLINE":
+ depth = 0
+ if prev_was_ws or token.at_line_start:
+ # ignore blank lines
+ continue
+ # pass the other cases on through
+ yield token
+ continue
+
+ # then it must be a real token (not WS, not NEWLINE)
+ # which can affect the indentation level
+
+ prev_was_ws = False
+ if token.must_indent:
+ # The current depth must be larger than the previous level
+ if not (depth > levels[-1]):
+ raise IndentationError("expected an indented block")
+
+ levels.append(depth)
+ yield INDENT(token.lineno)
+
+ elif token.at_line_start:
+ # Must be on the same level or one of the previous levels
+ if depth == levels[-1]:
+ # At the same level
+ pass
+ elif depth > levels[-1]:
+ raise IndentationError("indentation increase but not in new block")
+ else:
+ # Back up; but only if it matches a previous level
+ try:
+ i = levels.index(depth)
+ except ValueError:
+ raise IndentationError("inconsistent indentation")
+ for _ in range(i+1, len(levels)):
+ yield DEDENT(token.lineno)
+ levels.pop()
+
+ yield token
+
+ ### Finished processing ###
+
+ # Must dedent any remaining levels
+ if len(levels) > 1:
+ assert token is not None
+ for _ in range(1, len(levels)):
+ yield DEDENT(token.lineno)
+
+
+# The top-level filter adds an ENDMARKER, if requested.
+# Python's grammar uses it.
+def filter(lexer, add_endmarker = True):
+ token = None
+ tokens = iter(lexer.token, None)
+ tokens = track_tokens_filter(lexer, tokens)
+ for token in indentation_filter(tokens):
+ yield token
+
+ if add_endmarker:
+ lineno = 1
+ if token is not None:
+ lineno = token.lineno
+ yield _new_token("ENDMARKER", lineno)
+
+# Combine Ply and my filters into a new lexer
+
+class IndentLexer(object):
+ def __init__(self, debug=0, optimize=0, lextab='lextab', reflags=0):
+ self.lexer = lex.lex(debug=debug, optimize=optimize, lextab=lextab, reflags=reflags)
+ self.token_stream = None
+ def input(self, s, add_endmarker=True):
+ self.lexer.paren_count = 0
+ self.lexer.input(s)
+ self.token_stream = filter(self.lexer, add_endmarker)
+ def token(self):
+ try:
+ return self.token_stream.next()
+ except StopIteration:
+ return None
+
+########## Parser (tokens -> AST) ######
+
+# also part of Ply
+#import yacc
+
+# I use the Python AST
+from compiler import ast
+
+# Helper function
+def Assign(left, right):
+ names = []
+ if isinstance(left, ast.Name):
+ # Single assignment on left
+ return ast.Assign([ast.AssName(left.name, 'OP_ASSIGN')], right)
+ elif isinstance(left, ast.Tuple):
+ # List of things - make sure they are Name nodes
+ names = []
+ for child in left.getChildren():
+ if not isinstance(child, ast.Name):
+ raise SyntaxError("that assignment not supported")
+ names.append(child.name)
+ ass_list = [ast.AssName(name, 'OP_ASSIGN') for name in names]
+ return ast.Assign([ast.AssTuple(ass_list)], right)
+ else:
+ raise SyntaxError("Can't do that yet")
+
+
+# The grammar comments come from Python's Grammar/Grammar file
+
+## NB: compound_stmt in single_input is followed by extra NEWLINE!
+# file_input: (NEWLINE | stmt)* ENDMARKER
+def p_file_input_end(p):
+ """file_input_end : file_input ENDMARKER"""
+ print "end", p[1]
+ p[0] = ast.Stmt(p[1])
+
+def p_file_input(p):
+ """file_input : file_input NEWLINE
+ | file_input stmt
+ | NEWLINE
+ | stmt"""
+ if isinstance(p[len(p)-1], basestring):
+ if len(p) == 3:
+ p[0] = p[1]
+ else:
+ p[0] = [] # p == 2 --> only a blank line
+ else:
+ if len(p) == 3:
+ p[0] = p[1] + p[2]
+ else:
+ p[0] = p[1]
+
+
+# funcdef: [decorators] 'def' NAME parameters ':' suite
+# ignoring decorators
+def p_funcdef(p):
+ "funcdef : DEF NAME parameters COLON suite"
+ p[0] = ast.Function(None, p[2], list(p[3]), (), 0, None, p[5])
+
+# parameters: '(' [varargslist] ')'
+def p_parameters(p):
+ """parameters : LPAR RPAR
+ | LPAR varargslist RPAR"""
+ if len(p) == 3:
+ p[0] = []
+ else:
+ p[0] = p[2]
+
+
+# varargslist: (fpdef ['=' test] ',')* ('*' NAME [',' '**' NAME] | '**' NAME) |
+# highly simplified
+def p_varargslist(p):
+ """varargslist : varargslist COMMA NAME
+ | NAME"""
+ if len(p) == 4:
+ p[0] = p[1] + p[3]
+ else:
+ p[0] = [p[1]]
+
+# stmt: simple_stmt | compound_stmt
+def p_stmt_simple(p):
+ """stmt : simple_stmt"""
+ # simple_stmt is a list
+ p[0] = p[1]
+
+def p_stmt_compound(p):
+ """stmt : compound_stmt"""
+ p[0] = [p[1]]
+
+# simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE
+def p_simple_stmt(p):
+ """simple_stmt : small_stmts NEWLINE
+ | small_stmts SEMICOLON NEWLINE"""
+ p[0] = p[1]
+
+def p_small_stmts(p):
+ """small_stmts : small_stmts SEMICOLON small_stmt
+ | small_stmt"""
+ if len(p) == 4:
+ p[0] = p[1] + [p[3]]
+ else:
+ p[0] = [p[1]]
+
+# small_stmt: expr_stmt | print_stmt | del_stmt | pass_stmt | flow_stmt |
+# import_stmt | global_stmt | exec_stmt | assert_stmt
+def p_small_stmt(p):
+ """small_stmt : flow_stmt
+ | expr_stmt"""
+ p[0] = p[1]
+
+# expr_stmt: testlist (augassign (yield_expr|testlist) |
+# ('=' (yield_expr|testlist))*)
+# augassign: ('+=' | '-=' | '*=' | '/=' | '%=' | '&=' | '|=' | '^=' |
+# '<<=' | '>>=' | '**=' | '//=')
+def p_expr_stmt(p):
+ """expr_stmt : testlist ASSIGN testlist
+ | testlist """
+ if len(p) == 2:
+ # a list of expressions
+ #p[0] = ast.Discard(p[1])
+ p[0] = p[1]
+ else:
+ p[0] = Assign(p[1], p[3])
+
+def p_flow_stmt(p):
+ "flow_stmt : return_stmt"
+ p[0] = p[1]
+
+# return_stmt: 'return' [testlist]
+def p_return_stmt(p):
+ "return_stmt : RETURN testlist"
+ p[0] = ast.Return(p[2])
+
+
+def p_compound_stmt(p):
+ """compound_stmt : if_stmt
+ | funcdef"""
+ p[0] = p[1]
+
+def p_if_stmt(p):
+ 'if_stmt : IF test COLON suite'
+ p[0] = ast.If([(p[2], p[4])], None)
+
+def p_suite(p):
+ """suite : simple_stmt
+ | NEWLINE INDENT stmts DEDENT"""
+ if len(p) == 2:
+ p[0] = ast.Stmt(p[1])
+ else:
+ p[0] = ast.Stmt(p[3])
+
+
+def p_stmts(p):
+ """stmts : stmts stmt
+ | stmt"""
+ if len(p) == 3:
+ p[0] = p[1] + p[2]
+ else:
+ p[0] = p[1]
+
+## No using Python's approach because Ply supports precedence
+
+# comparison: expr (comp_op expr)*
+# arith_expr: term (('+'|'-') term)*
+# term: factor (('*'|'/'|'%'|'//') factor)*
+# factor: ('+'|'-'|'~') factor | power
+# comp_op: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in'|'is'|'is' 'not'
+
+def make_lt_compare(arg):
+ (left, right) = arg
+ return ast.Compare(left, [('<', right),])
+def make_gt_compare(arg):
+ (left, right) = arg
+ return ast.Compare(left, [('>', right),])
+def make_eq_compare(arg):
+ (left, right) = arg
+ return ast.Compare(left, [('==', right),])
+
+
+binary_ops = {
+ "+": ast.Add,
+ "-": ast.Sub,
+ "*": ast.Mul,
+ "/": ast.Div,
+ "<": make_lt_compare,
+ ">": make_gt_compare,
+ "==": make_eq_compare,
+}
+unary_ops = {
+ "+": ast.UnaryAdd,
+ "-": ast.UnarySub,
+ }
+precedence = (
+ ("left", "EQ", "GT", "LT"),
+ ("left", "PLUS", "MINUS"),
+ ("left", "MULT", "DIV"),
+ )
+
+def p_comparison(p):
+ """comparison : comparison PLUS comparison
+ | comparison MINUS comparison
+ | comparison MULT comparison
+ | comparison DIV comparison
+ | comparison LT comparison
+ | comparison EQ comparison
+ | comparison GT comparison
+ | PLUS comparison
+ | MINUS comparison
+ | power"""
+ if len(p) == 4:
+ p[0] = binary_ops[p[2]]((p[1], p[3]))
+ elif len(p) == 3:
+ p[0] = unary_ops[p[1]](p[2])
+ else:
+ p[0] = p[1]
+
+# power: atom trailer* ['**' factor]
+# trailers enables function calls. I only allow one level of calls
+# so this is 'trailer'
+def p_power(p):
+ """power : atom
+ | atom trailer"""
+ if len(p) == 2:
+ p[0] = p[1]
+ else:
+ if p[2][0] == "CALL":
+ if p[1].name == 'print':
+ p[0] = ast.Printnl(ast.Tuple(p[2][1]), None, None)
+ else:
+ p[0] = ast.CallFunc(p[1], p[2][1], None, None)
+ else:
+ raise AssertionError("not implemented")
+
+def p_atom_name(p):
+ """atom : NAME"""
+ p[0] = ast.Name(p[1])
+
+def p_atom_number(p):
+ """atom : NUMBER
+ | STRING"""
+ p[0] = ast.Const(p[1])
+
+def p_atom_tuple(p):
+ """atom : LPAR testlist RPAR"""
+ p[0] = p[2]
+
+# trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
+def p_trailer(p):
+ "trailer : LPAR arglist RPAR"
+ p[0] = ("CALL", p[2])
+
+# testlist: test (',' test)* [',']
+# Contains shift/reduce error
+def p_testlist(p):
+ """testlist : testlist_multi COMMA
+ | testlist_multi """
+ if len(p) == 2:
+ p[0] = p[1]
+ else:
+ # May need to promote singleton to tuple
+ if isinstance(p[1], list):
+ p[0] = p[1]
+ else:
+ p[0] = [p[1]]
+ # Convert into a tuple?
+ if isinstance(p[0], list):
+ p[0] = ast.Tuple(p[0])
+
+def p_testlist_multi(p):
+ """testlist_multi : testlist_multi COMMA test
+ | test"""
+ if len(p) == 2:
+ # singleton
+ p[0] = p[1]
+ else:
+ if isinstance(p[1], list):
+ p[0] = p[1] + [p[3]]
+ else:
+ # singleton -> tuple
+ p[0] = [p[1], p[3]]
+
+
+# test: or_test ['if' or_test 'else' test] | lambdef
+# as I don't support 'and', 'or', and 'not' this works down to 'comparison'
+def p_test(p):
+ "test : comparison"
+ p[0] = p[1]
+
+
+
+# arglist: (argument ',')* (argument [',']| '*' test [',' '**' test] | '**' test)
+# XXX INCOMPLETE: this doesn't allow the trailing comma
+def p_arglist(p):
+ """arglist : arglist COMMA argument
+ | argument"""
+ if len(p) == 4:
+ p[0] = p[1] + [p[3]]
+ else:
+ p[0] = [p[1]]
+
+# argument: test [gen_for] | test '=' test # Really [keyword '='] test
+def p_argument(p):
+ "argument : test"
+ p[0] = p[1]
+
+def p_error(p):
+ #print "Error!", repr(p)
+ raise SyntaxError(p)
+
+
+class GardenSnakeParser(object):
+ def __init__(self, lexer = None):
+ if lexer is None:
+ lexer = IndentLexer(debug=1)
+ self.lexer = lexer
+ self.parser = yacc.yacc(start="file_input_end")
+
+ def parse(self, code):
+ self.lexer.input(code)
+ result = self.parser.parse(lexer = self.lexer)
+ return ast.Module(None, result)
+
+
+###### Code generation ######
+
+from compiler import misc, syntax, pycodegen
+
+class GardenSnakeCompiler(object):
+ def __init__(self):
+ self.parser = GardenSnakeParser()
+ def compile(self, code, mode="exec", filename="<string>"):
+ tree = self.parser.parse(code)
+ print "snake"
+ pprint(tree)
+ misc.set_filename(filename, tree)
+ syntax.check(tree)
+ gen = pycodegen.ModuleCodeGenerator(tree)
+ code = gen.getCode()
+ return code
+
+####### Test code #######
+
+code = r"""
+
+print('LET\'S TRY THIS \\OUT')
+
+#Comment here
+def x(a):
+ print('called with', a)
+ if a == 1:
+ return 2
+ if a*2 > 10: return 999 / 4
+ # Another comment here
+
+ return a+2*3
+
+ints = (1, 2,
+ 3, 4,
+5)
+print('mutiline-expression', ints)
+
+if 1:
+ 8
+ a=9
+ print(x(a))
+
+t = 4+1/3*2+6*(9-5+1)
+print('predence test; should be 34+2/3:', t, t==(34+2/3))
+
+print('numbers', 1,2,3,4,5)
+
+print(x(1))
+print(x(2))
+print(x(8),'3')
+print('this is decimal', 1/5)
+print('BIG DECIMAL', 1.234567891234567)
+
+"""
+
+_code = """
+print('hello')
+if 1:
+ a=9
+"""
+
+_code = r"""
+
+def x(a):
+ y = 5
+ z = 5
+ print('called with', a)
+ return a*2
+
+print (x(1))
+"""
+
+lexer = IndentLexer(debug=1)
+# Give the lexer some input
+print "code"
+print code
+lexer.input(code)
+
+# Tokenize
+while True:
+ tok = lexer.token()
+ if not tok:
+ break # No more input
+ print(tok)
+
+# Set up the GardenSnake run-time environment
+def print_(*args):
+ print ("args", args)
+ print ("-->", " ".join(map(str,args)))
+
+#d = copy(globals())
+d = {}
+d["print"] = print_
+#d["a"] = 10
+l = {}
+
+
+compile = GardenSnakeCompiler().compile
+
+compiled_code = compile(code, mode="single", filename="string")
+
+from compiler import parse
+tree = parse(code, "exec")
+pprint(tree)
+
+print (compiled_code)
+
+exec (compiled_code, d)
+print ("Done")
+
+#print d
+#print l
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