Skip to content


Subversion checkout URL

You can clone with
Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

74 lines (64 sloc) 3.355 kB
import sys
import ASTNodes
from grammarExceptions import SemanticException
# Analyses the abstract syntax tree.
# Inputs are a symbolTable dictionary of form { id : ( id type, line number, assigned bool ) },
# the starting AST node and a flags dictionary of form { nodeType : info } where any relevant information
# for the particular node is set.
# Does not return anything. Will throw a semantic error if the code breaks the rules.
def analyse( symbolTable, node, flags ):
if node.getNodeType() == ASTNodes.STATEMENT_LIST:
analyse( symbolTable, node.getStatement(), flags )
analyse( symbolTable, node.getStatementList(), flags )
elif node.getNodeType() == ASTNodes.SPOKE:
spokeExpression = node.getExpression()
expType = analyse( symbolTable, spokeExpression, flags )
if spokeExpression.getNodeType() == ASTNodes.Factor:
if spokeExpression.getFactorType() == ASTNodes.ID:
(idType, lineNo, assigned) = symbolTable[spokeExpression.getValue()]
if not assigned:
raise SemanticException( node.lineno, node.clauseno )
idType = spokeExpression.getFactorType()
# If not a factor, must be of type number since letters are only
# valid as factors and not as part of operations or expressions.
idType = ASTNodes.NUMBER
flags[ASTNodes.SPOKE].add( idType )
elif node.getNodeType() == ASTNodes.ASSIGNMENT:
(identifier, expression) = node.children
expType = analyse( symbolTable, node.getExpression(), flags )
if expType == symbolTable[node.getVariable()][0]:
symbolTable[node.getVariable()][2] = True
raise SemanticException( node.lineno, node.clauseno )
elif node.getNodeType() == ASTNodes.TYPE:
return node.getType()
elif node.getNodeType() == ASTNodes.UNARY_OP:
expType = analyse( symbolTable, node.getExpression(), flags )
if expType == ASTNodes.NUMBER:
return expType
raise SemanticException( node.lineno, node.clauseno)
elif node.getNodeType() == ASTNodes.BINARY_OP:
leftExpType = analyse( symbolTable, node.getLeftExpression(), flags )
rightExpType = analyse( symbolTable, node.getRightExpression(), flags )
if leftExpType == rightExpType == ASTNodes.NUMBER:
return leftExpType
raise SemanticException( node.lineno, node.clauseno)
elif node.getNodeType() == ASTNodes.FACTOR:
if node.getFactorType() == ASTNodes.ID:
symbol = node.getValue()
if symbol in symbolTable:
(idType, lineNo, assigned ) = symbolTable[symbol]
if assigned:
return idType
raise SemanticException( node.lineno, node.clauseno)
return node.getFactorType()
elif node.getNodeType() == ASTNodes.DECLARATION:
variable = node.getVariable()
if variable in symbolTable:
raise SemanticException( node.lineno, node.clauseno, " You already told me what '%s' was on line %d" %(variable, symbolTable[variable][1]) )
symbolTable[variable] = [node.getExpression().getType(), node.lineno, True]
Jump to Line
Something went wrong with that request. Please try again.