The Theano <http://en.wikipedia.org/wiki/Theano_(Math_Compiler)> project that might be relevant in this discussion.
Theano is a python project that represents array computation as an abstract syntax tree of symbolic objects. It has a series of "optimizers" that walk over and change the graph on request. Its an interesting model and serves their purposes well. On Sun, Feb 26, 2012 at 8:35 PM, krastanov.ste...@gmail.com < krastanov.ste...@gmail.com> wrote: > I would like to point out that the immutability of the core need not > change if we follow the propositions in this discussion. > > In my opinion the important point here is the implementation of > abstract syntax trees for sympy. The minor (from mathematical point of > view) details about whether it should be immutable tree or whether > side effects and assignments should be allowed in the tree (hopefully > not!) are secondary. > > The use of ASTs seems like the right way to fix > http://code.google.com/p/sympy/issues/detail?id=1941 > > We can have identity crawler that does not change the tree (just > returns a copy). The current crawlers (just what Add and Mul do, but > much better abstracted). Simplification and canonization crawlers. > Special crawler options specific to an object (Units subclass politely > asking the crawler to be placed last). Now every time that we need > some canonization we subclass Expr. It is not a scalable solution at > all. > > Example: > Special treatment of Units in Mul > The subclassed Quantum Expr in the quantum module. > The need for MatExpr, MatAdd, MatMul... It is a good solution for the > current state of the code but it is ugly and it does not scale (what > happens when I want both matrices and kets in my expression?) > > The existence of AST would make the implementation of abstract > multilinear algebra or group theory much easier as there won't be any > need for subclassing Expr. Just writing a crawler for the tree should > be sufficient. It won't be less work, but the incompatibility between > the subclasses of Expr will be evaded. > > On 26 February 2012 16:58, Joachim Durchholz <j...@durchholz.org> wrote: >> Am 26.02.2012 20:05, schrieb Sergiu Ivanov: >> >>> As a functional programming beginner and fan, I can't but agree. I >>> was actually quite happy when I heard for the first time that SymPy >>> had immutable core, because that allows for much clearer and better >>> structured code (at least I see it so). >> >> >> Hm... there's the question what an "immutable core" actually is. Is it the >> mathematical objects that the user sees, or is it an internal API for >> programmers? >> >> In the former case, I'd avoid mutability. It's just a conceptual hassle, it >> makes semantics-preserving transformations harder (as soon as references are >> involved, prohibitively hard for a project of SymPy's scale - you need alias >> analysis, and compiler teams spend person-decades on that kind of stuff). >> >> In the latter case, there's nothing wrong with it. Sure, coding just with >> immutable data is fun and far less error-prone, but Python is not built for >> that coding style; I suspect such code would be very clean but not very >> efficient. >> >> >>> I'd like to ask the question which I believe to be very important: >>> what would be the benefit of having a mutable core? >> >> >> That's an interesting question, yes. >> And the first one that should be asked whenever important changes are >> undertaken, and the first one to look for an answer for. >> >> Just my 2c. >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sympy" group. >> 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. >> > > -- > You received this message because you are subscribed to the Google Groups "sympy" group. > 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. > -- You received this message because you are subscribed to the Google Groups "sympy" group. 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.
