On Sunday, March 11, 2012 7:00:15 PM UTC+5:30, Joachim Durchholz wrote: > > Am 11.03.2012 05:27, schrieb Bharath M R: > > @Sergiu I was looking at top down operator precedence parsing for the > task > > That's the technique where the grammar requires the least contortions. > It also composes well: you can define sublanguages (such as arithmetic > and boolean logic), and as long as their operator sets do not overlap, > you can combine them without any problems. > > It is a bit restricted in what classes of languages it can handle. > Parsing a*-b is not possible but can be enabled using a hack. > I don't know how to parse http://en.wikipedia.org/wiki/Bra-ket_notation > using operator precedence. > > > (http://javascript.crockford.com/tdop/tdop.html) . > > Crockford is very wrong that operator-precedence parsing is in any way > connected to dynamic languages. > > In general, he's not exposing principles but presenting a recipe. I > don't think that's easy to transfer to Python code. > > > One of the important task is to > > come up with the grammar. > > Not for operator-precedence grammars! > You need: > - a list of precedence levels, > - for each level: > - the list of operators > - whether it's left, right, or non-associative > - a list of left and right parentheses > > The problem with unary minus is that it has a different precedence than > binary minus. The standard approach is to let the tokenizer detect > multiple operator symbols in a row, and emit a different pseudo-minus > token whenever it isn't the first. > I'm pretty sure I could whip up a systematic approach that would cover > more operators and hold up in the presence of postfix operators, but I > don't know whether that's even relevant in SymPy. (The only postfix > operator in widespread use I know about is !, and that isn't used as an > infix operator.) > Thanks for the reply. The parser is for building the web interface similar to Wolfram Alpha for SymPy. Basically I want to parse things like integrate x**2 dx roots x**2==1
Won't the operator precedence parsing be sufficient for this? If it is not, can you help me with some reading material on some parsing technique which can acomplish this. Thanks, Bharath M R -- You received this message because you are subscribed to the Google Groups "sympy" group. To view this discussion on the web visit https://groups.google.com/d/msg/sympy/-/Xn1LJmMSOJAJ. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
