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     INTRO(9)                                                 INTRO(9)

          intro - introduction to Inferno Tk

          This section of the manual provides a reference for the
          Inferno Tk implementation, which is accessed by Limbo
          programs via tk(2), and from sh(1) via sh-tk(1).

          The following pages were derived by Vita Nuova from documen-
          tation that is

               Copyright © 1990 The Regents of the University of Cali-
               Copyright © 1994-1996 Sun Microsystems, Inc.
               See copyright(9) for the full copyright notice.

          The format of the pages has changed to follow the format of
          the rest of this manual, but more important, the content has
          been changed (typically in small ways) to reflect the vari-
          ant of Tk implemented by Inferno.

        Programming Interface
          The interface to Inferno Tk is exclusively through the tk(2)
          module; all the Tk commands described in this section of the
          manual are excecuted by passing them as strings to the cmd
          function in that module.  The Inferno Tk implementation is
          based on the Tk 4.0 documentation, but there are many dif-
          ferences, probably the greatest of which is that there is no
          associated Tcl implementation, so almost every Inferno
          application using Tk will need to have some Limbo code asso-
          ciated with it (the sh-tk(1) shell module can also fulful
          this rôle). See ``An Overview of Limbo/Tk'' in Volume 2 for
          a tutorial-style introduction to the use of Inferno Tk which
          summarises the differences from Tk 4.0.

        Tk Commands
          The command string passed to tk->cmd may contain one or more
          Tk commands, separated by semicolons.  A semicolon is not a
          command separator when it is nested in braces ({}) or brack-
          ets ([]) or it is escaped by a backslash (\).  Each command
          is divided into words: sequences of characters separated by
          one or more blanks and tabs.

          There is also a `super quote' convention: at any point in
          the command string a single quote mark (') means that the
          entire rest of the string should be treated as one word.

          A word beginning with an opening brace ({) continues until
          the balancing closing brace (}) is reached. The outer brace
          characters are stripped. A backslash can be used to escape a

     INTRO(9)                                                 INTRO(9)

          brace in this context. Backslash characters not used to
          escape braces are left unchanged.

          A word beginning with an opening bracket ([) continues until
          the balancing closing bracket (]) is reached. The enclosed
          string is then evaluated as if it were a command string, and
          the resulting value is used as the contents of the word.

          Single commands are executed in order until they are all
          done or an error is encountered. By convention, an error is
          signaled by a return value starting with an exclamation mark
          (!).  The return value from tk->cmd is the return value of
          the first error-producing command or else the return value
          of the final single command.

          To execute a single command, the first word is examined. It
          must either begin with dot (.)  in which case it must name
          an existing widget, which will interpret the rest of the
          command according to its type, or one of the following
          words, each of which is documented in a manual page of that
          name in this section:
          button      entry       listbox     destroy
          menu        scale       pack        image
          canvas      frame       bind        update
          menubutton  scrollbar   focus       send
          checkbutton label       grab        variable
          radiobutton text        cursor

        Widget Options
          Each manual page in this section documents the options that
          a particular command will accept. A number of options are
          common to several of the widgets and are named as ``standard
          options'' near the beginning of the manual page for each
          widget. These options are documented in options(9). The
          types of value required as arguments to options within
          Inferno Tk are documented under types(9).

          options(9), types(9), tk(2), sh-tk(1), tkcmd(1), wmlib(2),
          draw-intro(2), ``An Overview of Limbo/Tk'' in Volume 2.

          The bracket ([]) command interpretation is not applied con-
          sistently throughout the Inferno Tk commands (notably, the
          argument to the send(9) command will not interpret this cor-
          rectly).  Moreover, if the string to be substituted is sig-
          nificantly bigger than the command it was substituting, then
          it will be truncated.