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https://github.com/CHOMPStation2/CHOMPStation2.git
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310 lines
9.6 KiB
Plaintext
310 lines
9.6 KiB
Plaintext
/*
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File: Expressions
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Procedures for parsing expressions.
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*/
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/*
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Macros: Expression Macros
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OPERATOR - A value indicating the parser currently expects a binary operator.
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VALUE - A value indicating the parser currently expects a value.
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SHIFT - Tells the parser to push the current operator onto the stack.
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REDUCE - Tells the parser to reduce the stack.
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*/
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#define OPERATOR 1
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#define VALUE 2
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#define SHIFT 0
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#define REDUCE 1
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/*
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Class: nS_Parser
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*/
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/n_Parser/nS_Parser
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/*
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Var: expecting
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A variable which keeps track of whether an operator or value is expected. It should be either <OPERATOR> or <VALUE>. See <ParseExpression()>
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for more information.
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*/
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var/expecting=VALUE
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/*
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Proc: Precedence
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Compares two operators, decides which is higher in the order of operations, and returns <SHIFT> or <REDUCE>.
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*/
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/n_Parser/nS_Parser/proc/Precedence(node/expression/operator/top, node/expression/operator/input)
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if(istype(top))
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top=top.precedence
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if(istype(input))
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input=input:precedence
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if(top>=input)
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return REDUCE
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return SHIFT
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/*
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Proc: GetExpression
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Takes a token expected to represent a value and returns an <expression> node.
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*/
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/n_Parser/nS_Parser/proc/GetExpression(token/T)
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if(!T) return
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if(istype(T, /node/expression))
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return T
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switch(T.type)
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if(/token/word)
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return new/node/expression/value/variable(T.value)
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if(/token/accessor)
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var/token/accessor/A=T
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var/node/expression/value/variable/E//=new(A.member)
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var/stack/S=new()
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while(istype(A.object, /token/accessor))
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S.Push(A)
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A=A.object
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ASSERT(istext(A.object))
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while(A)
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var/node/expression/value/variable/V=new()
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V.id=new(A.member)
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if(E)
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V.object=E
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else
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V.object=new/node/identifier(A.object)
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E=V
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A=S.Pop()
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return E
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if(/token/number, /token/string)
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return new/node/expression/value/literal(T.value)
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/*
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Proc: GetOperator
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Gets a path related to a token or string and returns an instance of the given type. This is used to get an instance of either a binary or unary
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operator from a token.
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Parameters:
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O - The input value. If this is a token, O is reset to the token's value.
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When O is a string and is in L, its associated value is used as the path to instantiate.
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type - The desired type of the returned object.
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L - The list in which to search for O.
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See Also:
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- <GetBinaryOperator()>
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- <GetUnaryOperator()>
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*/
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/n_Parser/nS_Parser/proc/GetOperator(O, type=/node/expression/operator, L[])
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if(istype(O, type)) return O //O is already the desired type
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if(istype(O, /token)) O=O:value //sets O to text
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if(istext(O)) //sets O to path
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if(L.Find(O)) O=L[O]
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else return null
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if(ispath(O))O=new O //catches path from last check
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else return null //Unknown type
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return O
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/*
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Proc: GetBinaryOperator
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Uses <GetOperator()> to search for an instance of a binary operator type with which the given string is associated. For example, if
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O is set to "+", an <Add> node is returned.
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See Also:
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- <GetOperator()>
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- <GetUnaryOperator()>
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*/
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/n_Parser/nS_Parser/proc/GetBinaryOperator(O)
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return GetOperator(O, /node/expression/operator/binary, options.binary_operators)
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/*
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Proc: GetUnaryOperator
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Uses <GetOperator()> to search for an instance of a unary operator type with which the given string is associated. For example, if
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O is set to "!", a <LogicalNot> node is returned.
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See Also:
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- <GetOperator()>
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- <GetBinaryOperator()>
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*/
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/n_Parser/nS_Parser/proc/GetUnaryOperator(O)
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return GetOperator(O, /node/expression/operator/unary, options.unary_operators)
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/*
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Proc: Reduce
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Takes the operator on top of the opr stack and assigns its operand(s). Then this proc pushes the value of that operation to the top
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of the val stack.
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*/
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/n_Parser/nS_Parser/proc/Reduce(stack/opr, stack/val)
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var/node/expression/operator/O=opr.Pop()
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if(!O) return
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if(!istype(O))
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errors+=new/scriptError("Error reducing expression - invalid operator.")
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return
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//Take O and assign its operands, popping one or two values from the val stack
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//depending on whether O is a binary or unary operator.
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if(istype(O, /node/expression/operator/binary))
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var/node/expression/operator/binary/B=O
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B.exp2=val.Pop()
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B.exp =val.Pop()
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val.Push(B)
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else
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O.exp=val.Pop()
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val.Push(O)
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/*
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Proc: EndOfExpression
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Returns true if the current token represents the end of an expression.
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Parameters:
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end - A list of values to compare the current token to.
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*/
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/n_Parser/nS_Parser/proc/EndOfExpression(end[])
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if(!curToken)
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return 1
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if(istype(curToken, /token/symbol) && end.Find(curToken.value))
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return 1
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if(istype(curToken, /token/end) && end.Find(/token/end))
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return 1
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return 0
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/*
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Proc: ParseExpression
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Uses the Shunting-yard algorithm to parse expressions.
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Notes:
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- When an opening parenthesis is found, then <ParseParenExpression()> is called to handle it.
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- The <expecting> variable helps distinguish unary operators from binary operators (for cases like the - operator, which can be either).
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Articles:
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- <http://epaperpress.com/oper/>
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- <http://en.wikipedia.org/wiki/Shunting-yard_algorithm>
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See Also:
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- <ParseFunctionExpression()>
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- <ParseParenExpression()>
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- <ParseParamExpression()>
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*/
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/n_Parser/nS_Parser/proc/ParseExpression(list/end=list(/token/end), list/ErrChars=list("{", "}"))
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var/stack/opr=new
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var/stack/val=new
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src.expecting=VALUE
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while(TRUE)
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if(EndOfExpression(end))
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break
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if(istype(curToken, /token/symbol) && ErrChars.Find(curToken.value))
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errors+=new/scriptError/BadToken(curToken)
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break
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if(index>tokens.len) //End of File
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errors+=new/scriptError/EndOfFile()
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break
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var/token/ntok
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if(index+1<=tokens.len)
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ntok=tokens[index+1]
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if(istype(curToken, /token/symbol) && curToken.value=="(") //Parse parentheses expression
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if(expecting!=VALUE)
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errors+=new/scriptError/ExpectedToken("operator", curToken)
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NextToken()
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continue
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val.Push(ParseParenExpression())
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else if(istype(curToken, /token/symbol)) //Operator found.
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var/node/expression/operator/curOperator //Figure out whether it is unary or binary and get a new instance.
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if(src.expecting==OPERATOR)
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curOperator=GetBinaryOperator(curToken)
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if(!curOperator)
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errors+=new/scriptError/ExpectedToken("operator", curToken)
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NextToken()
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continue
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else
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curOperator=GetUnaryOperator(curToken)
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if(!curOperator) //given symbol isn't a unary operator
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errors+=new/scriptError/ExpectedToken("expression", curToken)
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NextToken()
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continue
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if(opr.Top() && Precedence(opr.Top(), curOperator)==REDUCE) //Check order of operations and reduce if necessary
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Reduce(opr, val)
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continue
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opr.Push(curOperator)
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src.expecting=VALUE
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else if(ntok && ntok.value=="(" && istype(ntok, /token/symbol)\
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&& istype(curToken, /token/word)) //Parse function call
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var/token/preToken=curToken
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var/old_expect=src.expecting
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var/fex=ParseFunctionExpression()
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if(old_expect!=VALUE)
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errors+=new/scriptError/ExpectedToken("operator", preToken)
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NextToken()
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continue
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val.Push(fex)
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else if(istype(curToken, /token/keyword)) //inline keywords
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var/n_Keyword/kw=options.keywords[curToken.value]
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kw=new kw(inline=1)
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if(kw)
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if(!kw.Parse(src))
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return
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else
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errors+=new/scriptError/BadToken(curToken)
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else if(istype(curToken, /token/end)) //semicolon found where it wasn't expected
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errors+=new/scriptError/BadToken(curToken)
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NextToken()
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continue
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else
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if(expecting!=VALUE)
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errors+=new/scriptError/ExpectedToken("operator", curToken)
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NextToken()
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continue
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val.Push(GetExpression(curToken))
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src.expecting=OPERATOR
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NextToken()
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while(opr.Top()) Reduce(opr, val) //Reduce the value stack completely
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.=val.Pop() //Return what should be the last value on the stack
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if(val.Top()) //
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var/node/N=val.Pop()
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errors+=new/scriptError("Error parsing expression. Unexpected value left on stack: [N.ToString()].")
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return null
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/*
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Proc: ParseFunctionExpression
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Parses a function call inside of an expression.
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See Also:
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- <ParseExpression()>
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*/
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/n_Parser/nS_Parser/proc/ParseFunctionExpression()
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var/node/expression/FunctionCall/exp=new
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exp.func_name=curToken.value
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NextToken() //skip function name
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NextToken() //skip open parenthesis, already found
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var/loops = 0
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while(TRUE)
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loops++
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if(loops>=1000)
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CRASH("Something TERRIBLE has gone wrong in ParseFunctionExpression ;__;")
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if(istype(curToken, /token/symbol) && curToken.value==")")
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return exp
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exp.parameters+=ParseParamExpression()
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if(curToken.value==","&&istype(curToken, /token/symbol))NextToken() //skip comma
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if(istype(curToken, /token/end)) //Prevents infinite loop...
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errors+=new/scriptError/ExpectedToken(")")
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return exp
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/*
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Proc: ParseParenExpression
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Parses an expression that ends with a close parenthesis. This is used for parsing expressions inside of parentheses.
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See Also:
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- <ParseExpression()>
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*/
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/n_Parser/nS_Parser/proc/ParseParenExpression()
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if(!CheckToken("(", /token/symbol))
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return
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return new/node/expression/operator/unary/group(ParseExpression(list(")")))
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/*
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Proc: ParseParamExpression
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Parses an expression that ends with either a comma or close parenthesis. This is used for parsing the parameters passed to a function call.
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See Also:
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- <ParseExpression()>
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*/
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/n_Parser/nS_Parser/proc/ParseParamExpression()
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return ParseExpression(list(",", ")")) |