Bug in printing symbolic derivative (PR#1697)

[Peter Dalgaard BSA]

murdoch@stats.uwo.ca writes:


> > eval(Dxy)
> [1] 0.1098938  # this is right
> > eval(Dyx)
> [1] 0.1098938  # this is right
> > -exp(-2 * x * y) * (-2 * x) * (2 * y) + exp(-2 * x * y) * 2 # this is how Dxy prints
> [1] 0.1831564  # this is wrong!!
> > -(exp(-2 * x * y) * (-2 * x) * (2 * y) + exp(-2 * x * y) * 2) # this is how it should print
> [1] 0.1098938  # this is right
> 
> Looks like that's it...

Yep. This is another long-standing item on the parse/deparse TODO
list. A more minimalistic version is

> "*"(5,2+3)
[1] 25
> quote("*"(5,2+3))
5 * 2 + 3
> eval(quote("*"(5,2+3)))
[1] 25

There are really two issues: we don't strip parentheses when parsing
and we don't insert them where needed on deparsing.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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