Re: problem writing debugging utility function

*To*: mathgroup at smc.vnet.net*Subject*: [mg100274] Re: problem writing debugging utility function*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Sun, 31 May 2009 06:31:05 -0400 (EDT)*References*: <gvq09k$mqv$1@smc.vnet.net>

dabrowsa at indiana.edu wrote: > This matter is pretty unimportant, but perhaps of interest in laying > out a persistent source confusion for me with Mathematica: evaluation > control. > > I'm skeptical of the built-in debugger because it seems to crash the > kernel often, so I do most of my debugging by inserting print > statements like > > Print["variableOne = ",variableOne]. > > Being extraordinarily lazy I soon thought it might be nice to have a > little function, say dbgv, which takes a variable or name of a > variable as an argument, and produces the same result as the print > statement above. > > At first I assumed this would be easy, since almost every programming > problem turns out to be pretty easy with Mathematica. But after an hour > or so I began to wonder whether it would be possible at all. I did > eventually find a solution, a function dbgv such that dbgv[variableOne] > produces exactly the effect of the print statement, but it's really ugly. > I'll post it later. > > Granted this is not an important problem since it's not too much > trouble to just type in the whole print statement. But it's worth > noting that this would trivial to solve with a Lisp macro, and despite > the fantastic expressibility of Mathematica it doesn't seem to have a > good replacement for macros. The closest equivalents are $Pre(Read), > which I used in my solution, but they're not nearly as nice to work with. > > Can anyone think of an elegant solution? > For a function that works like the Print expression above, one could use one of the following: Non-string version: SetAttributes[dbg, HoldAll] dbg[var_] := Print[ToString[Unevaluated[var]], " = ", var] String version: dbg2[name_String] := ToExpression[name, InputForm, Print[name, " = ", #] &] Though I am not sure I understand your question because I don't see what relation $Pre or Read have with this. For debugging, take a look at Trace, On[] and Off[], and Monitor as well.