Re: beginner question about syntax

*To*: mathgroup at smc.vnet.net*Subject*: [mg109086] Re: beginner question about syntax*From*: dr DanW <dmaxwarren at gmail.com>*Date*: Mon, 12 Apr 2010 22:59:19 -0400 (EDT)*References*: <hputp3$lh7$1@smc.vnet.net>

AK, Whenever Mathematica seems to be doing something nonsensical (based on what you are seeing on the screen,) then FullForm[] is your friend. What you see in your notebook are expressions formatted to be human- readable. FullForm[] lets you see the structure that Mathematica is actually working with. In[14]:= FullForm[a] Out[14]//FullForm= a In[15]:= FullForm[a + b + c] Out[15]//FullForm= Plus[a, b, c] Mathematica expressions are always in the form of head[elem1, elem2, ...]. Of course, you may not see that structure explicitly unless you use FullForm[]. The function Map[f, expr] applies f to each element on the first level in expr. Looking at the FullForm of a, you see that a has no first level (it is all head), thus there is nothing to Map f to. Plus[a,b,c] has the head Plus and three elements (a, b, and c) at the first level, so f gets mapped to them. Hope this helps, Daniel