Common errors

When wrapping a line, make sure to end with an operator on the line to be continued,
expr + newline
expr
Whereas this appears to the R interpreter as two seperate expressions on two different lines
expr newline
+ expr
Related: While the else keyword and clause behaves properly when encapsulated in a function,
In file etest.R:
```
etest <- function( k )
   {
    if ( k > 0 )
       {  cat("k is greater than 0\n" )  }
    else
       {  cat("k is NOT greater than 0\n" )   }
   }
```
Execution:
```
> source("etest.R")
> etest(0) 
k is NOT greater than 0
> etest(1)
k is greater than 0
```
The same example also works when the entire function is typed directly to the command line interpreter.

But beware: this behavior changes outside the body of the function definition. When typing directly to the command line interpreter, or more importantly, when sourcing a file with the else keyword begining on a new line, a syntax error results:
contents of file etest2.R:
```
if ( k > 0 )
   {  cat("k is greater than 0\n" )  }
else
   {  cat("k is NOT greater than 0\n" )   }
```
when this is sourced,
```
> source("etest2.R")
Error in parse(file, n = -1, NULL, "?") : syntax error at
3:    {  cat("k is greater than 0\n" )  }
4: else
```
This is because outside of function definitions, the parser is looking for the first complete command it finds at the end of each newline. This can be prevented by putting the else clause on the same line as the } that ends the then clause:
```
k <- 0

if ( k > 0 ) {
    cat("k is greater than 0\n" )  
} else {
    cat("k is NOT greater than 0\n" )   
}
```
when this is sourced, it works properly
```
> source("etest3.R")
k is NOT greater than 0
```
see Discussion at list R-help
when using hist() to make histograms of quantities q which will include 0 (zero), you must make the breaks range start below 0 to prevent the zero bin from being treated as a underflow and thus get added to the next bin
```
        hist( q, -1:max(q) )
```
When making a list of lists using rep() or c(), its necessary to put one more encapsulation of list()
```
bugs <- list( list(dels=c(),silents=c()) )
for ( i in 2:n_bugs )                                
    bugs <- c( bugs, list( list(dels=c(),silents=c()) ) )
```
to make a list of lists with initial empty members:
gens <- rep( list( list( dels=c(), sils=c() ) ), n_gens )