149 lines
3.5 KiB
Python
149 lines
3.5 KiB
Python
from fol.node import Node
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class Parser:
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def __init__(self, lexer):
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self.lexer = lexer
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def consume(self, name):
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tok = self.lexer.peek()
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if tok and tok.is_a(name):
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self.lexer.next()
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return tok
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return None
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def ensure(self, name):
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tok = self.consume(name)
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if tok is None:
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raise Exception(f'invalid {name}')
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if tok and not tok.is_a(name):
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raise Exception(f'expected {name}, got {tok.name}')
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return tok
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def parse(self):
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return self.parse_f()
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def parse_f(self):
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return self.parse_exists()
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def parse_exists(self):
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if self.consume('EXISTS'):
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tok_var = self.ensure('VAR')
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rhs = self.parse_forall()
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node = Node('EXISTS')
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node.add_child(Node('VAR', tok_var.value))
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node.add_child(rhs)
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return node
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return self.parse_forall()
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def parse_forall(self):
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if self.consume('FORALL'):
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tok_var = self.ensure('VAR')
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rhs = self.parse_imp()
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node = Node('FORALL')
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node.add_child(Node('VAR', tok_var.value))
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node.add_child(rhs)
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return node
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return self.parse_imp()
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def parse_imp(self):
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lhs = self.parse_or()
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if self.consume('IMP'):
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rhs = self.parse_or()
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node = Node('IMP')
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node.add_child(lhs)
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node.add_child(rhs)
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lhs = node
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return lhs
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def parse_or(self):
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lhs = self.parse_and()
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while self.consume('OR'):
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rhs = self.parse_and()
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node = Node('OR')
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node.add_child(lhs)
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node.add_child(rhs)
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lhs = node
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return lhs
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def parse_and(self):
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lhs = self.parse_not()
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while self.consume('AND'):
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rhs = self.parse_not()
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node = Node('AND')
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node.add_child(lhs)
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node.add_child(rhs)
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lhs = node
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return lhs
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def parse_not(self):
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if self.consume('NOT'):
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node = Node('NOT')
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node.add_child(self.parse_group())
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return node
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return self.parse_group()
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def parse_group(self):
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if self.consume('OPAR'):
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node = self.parse_f()
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self.ensure('CPAR')
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return node
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return self.parse_pred()
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def parse_pred(self):
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tok = self.ensure('PRED')
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self.ensure('OPAR')
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node = Node('PRED', tok.value)
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node.add_child(self.parse_term())
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while self.consume('COMMA'):
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node.add_child(self.parse_term())
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self.ensure('CPAR')
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return node
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def parse_term(self):
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maybe_var = self.lexer.peek(0)
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maybe_opar = self.lexer.peek(1)
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if maybe_var and maybe_opar and maybe_var.is_a('VAR') \
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and maybe_opar.is_a('OPAR'):
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return self.parse_function()
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tok = self.lexer.next()
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if tok is None:
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raise Exception('unexpected end')
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if tok.name in ['VAR', 'CONST']:
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return Node(tok.name, tok.value)
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raise Exception(f'unknown term {tok.value}')
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def parse_function(self):
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tok = self.ensure('VAR')
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self.ensure('OPAR')
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node = Node('FUN', tok.value)
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node.add_child(self.parse_term())
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while self.consume('COMMA'):
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node.add_child(self.parse_term())
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self.ensure('CPAR')
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return node
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