[R] check variables: a Q from a beginner

[Yan Yu]

HI, all,
How can i check the variables that is currently being loaded..
ls() only list the variable name, but not the summary of the variable,
like the dimension of the variable etc.. Is there a command in R, which
is equivalent to "whos" in matlab, which let me check the variables
currently loaded in Matlab..
also, Does anyone have recommendation on ~a good reference to R..
I could not find the answer to my Q in the documentation included with R
package..

thanks,
yan