[LET] variable-name = expression

   Synopsis:
      Assigns the value of a (scalar) variable

   Notes:
      In scripts without line numbers, variables must be assigned values with
         LET, unless an OPTION NOLET statement appears in the script.
      In scripts with line numbers, the LET keyword is optional.

   Examples:
      LET greeting$ = "Hello world!"
      LET myarray (5) = 100

      OPTION NOLET
      greeting$ = "Hello world!"
      myarray (5) = 100

      10 a$ = "hello world!"
      10 LET a$ = "hello world!"
