Mathias, If it's any comfort, I appreciated the example; 'expected' behaviour maybe, but a very nice example for staff/student training!
S Ellison > -----Original Message----- > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Matthias > Gondan > Sent: 02 September 2017 18:22 > To: r-help@r-project.org > Subject: [R] Strange lazy evaluation of default arguments > > Dear R developers, > > sessionInfo() below > > Please have a look at the following two versions of the same function: > > 1. Intended behavior: > > > Su1 = function(u=100, l=u, mu=0.53, sigma2=4.3^2) > + { > + print(c(u, l, mu)) # here, l is set to u’s value > + u = u/sqrt(sigma2) > + l = l/sqrt(sigma2) > + mu = mu/sqrt(sigma2) > + print(c(u, l, mu)) > + } > > > > Su1() > [1] 100.00 100.00 0.53 > [1] 23.2558140 23.2558140 0.1232558 > > In the first version, both u and l are correctly divided by 4.3. > > 2. Strange behavior: > > > Su2 = function(u=100, l=u, mu=0.53, sigma2=4.3^2) > + { > + # print(c(u, l, mu)) > + u = u/sqrt(sigma2) > + l = l/sqrt(sigma2) # here, l is set to u’s value > + mu = mu/sqrt(sigma2) > + print(c(u, l, mu)) > + } > > > > Su2() > [1] 23.2558140 5.4083288 0.1232558 > In the second version, the print function is commented out, so the variable u > is copied to l (lowercase L) at a later place, and L is divided twice by 4.3. > > Is this behavior intended? It seems strange that the result depends on a > debugging message. > > Best wishes, > > Matthias > > > > sessionInfo() > R version 3.4.1 (2017-06-30) > Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows >= 8 > x64 (build 9200) > > Matrix products: default > > locale: > [1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252 > LC_MONETARY=German_Germany.1252 > [4] LC_NUMERIC=C LC_TIME=German_Germany.1252 > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > loaded via a namespace (and not attached): > [1] compiler_3.4.1 tools_3.4.1 > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. ******************************************************************* This email and any attachments are confidential. Any use, copying or disclosure other than by the intended recipient is unauthorised. If you have received this message in error, please notify the sender immediately via +44(0)20 8943 7000 or notify postmas...@lgcgroup.com and delete this message and any copies from your computer and network. LGC Limited. Registered in England 2991879. Registered office: Queens Road, Teddington, Middlesex, TW11 0LY, UK ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
