Technically S-PLUS is a function language with a very simple syntax. It is case sensitive as are most UNIX based packages, so A and a are different variables.
Elementary commands consist of either expressions or assignments. If an expression is given as a command, it is evaluated, printed, and the value is lost. An assignment also evaluates an expression and passes the value to a variable but the result is not printed automatically.
Commands are separated either by a semi-colon, ;, or by a newline. If a command is not complete at the end of a line, S-PLUS will give a different prompt, for example
on second and subsequent lines and continue to read input until the command is syntactically complete. This prompt may also be changed if the user wishes. In these notes we will generally omit the continuation prompt and indicate continuation by simple indenting.