Sources specified lines within a single file.
     
    
    Usage
    source_lines(file, lines, env)
 
    
    Arguments
- file
- a connection object or a character string path to a file. 
- lines
- A vector of integers specifying the lines to be sourced. 
- env
- the environment in which to source the lines. 
 
    
    Value
    No return value, called for side effects.
     
    
    IMPORTANT !!!
    Sourcing this file is a mistake - may result in infinite recursion.