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8be014ee46
This directory now contains third_party software that is vendored into the Servo source tree. The idea is that it would eventually hold webrender and other crates from mozilla-central as well with a standard patch management approach for each.
133 lines
2.5 KiB
Python
133 lines
2.5 KiB
Python
# -----------------------------------------------------------------------------
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# calc.py
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#
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# A simple calculator with variables. This is from O'Reilly's
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# "Lex and Yacc", p. 63.
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#
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# This example uses unicode strings for tokens, docstrings, and input.
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# -----------------------------------------------------------------------------
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import sys
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sys.path.insert(0, "../..")
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tokens = (
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'NAME', 'NUMBER',
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'PLUS', 'MINUS', 'TIMES', 'DIVIDE', 'EQUALS',
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'LPAREN', 'RPAREN',
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)
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# Tokens
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t_PLUS = ur'\+'
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t_MINUS = ur'-'
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t_TIMES = ur'\*'
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t_DIVIDE = ur'/'
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t_EQUALS = ur'='
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t_LPAREN = ur'\('
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t_RPAREN = ur'\)'
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t_NAME = ur'[a-zA-Z_][a-zA-Z0-9_]*'
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def t_NUMBER(t):
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ur'\d+'
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try:
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t.value = int(t.value)
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except ValueError:
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print "Integer value too large", t.value
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t.value = 0
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return t
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t_ignore = u" \t"
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def t_newline(t):
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ur'\n+'
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t.lexer.lineno += t.value.count("\n")
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def t_error(t):
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print "Illegal character '%s'" % t.value[0]
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t.lexer.skip(1)
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# Build the lexer
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import ply.lex as lex
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lex.lex()
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# Parsing rules
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precedence = (
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('left', 'PLUS', 'MINUS'),
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('left', 'TIMES', 'DIVIDE'),
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('right', 'UMINUS'),
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)
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# dictionary of names
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names = {}
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def p_statement_assign(p):
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'statement : NAME EQUALS expression'
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names[p[1]] = p[3]
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def p_statement_expr(p):
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'statement : expression'
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print p[1]
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def p_expression_binop(p):
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'''expression : expression PLUS expression
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| expression MINUS expression
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| expression TIMES expression
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| expression DIVIDE expression'''
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if p[2] == u'+':
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p[0] = p[1] + p[3]
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elif p[2] == u'-':
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p[0] = p[1] - p[3]
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elif p[2] == u'*':
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p[0] = p[1] * p[3]
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elif p[2] == u'/':
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p[0] = p[1] / p[3]
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def p_expression_uminus(p):
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'expression : MINUS expression %prec UMINUS'
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p[0] = -p[2]
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def p_expression_group(p):
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'expression : LPAREN expression RPAREN'
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p[0] = p[2]
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def p_expression_number(p):
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'expression : NUMBER'
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p[0] = p[1]
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def p_expression_name(p):
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'expression : NAME'
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try:
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p[0] = names[p[1]]
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except LookupError:
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print "Undefined name '%s'" % p[1]
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p[0] = 0
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def p_error(p):
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if p:
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print "Syntax error at '%s'" % p.value
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else:
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print "Syntax error at EOF"
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import ply.yacc as yacc
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yacc.yacc()
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while 1:
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try:
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s = raw_input('calc > ')
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except EOFError:
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break
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if not s:
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continue
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yacc.parse(unicode(s))
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