Ada95 Binding for ncurses

by Jürgen Pfeifer.

General Remarks

• This document describes Version 01.00 of the binding.
• The functionality is modeled to be compatible with the ncurses package, a clone of the SVr4 curses model.
  I did the development on an Intel box running the latest stable release of Linux, ncurses and the most recent released GNU Ada Translator gnat versions. For any older versions of ncurses and gnat it is not guaranteed to work.
• You must have the m4 macroprocessor to build this package. If you don't have this program, you can get the FSF version here.
• Ada programs are supposed to be readable. One of my favorite methods to make code readable is to use expressive names for the identifiers. You can find a list of a mapping of the cryptic curses names to the Ada names in this table.
• This is not a typical one-to-one interface mapping. It is close to one-to-one on the functional level. Each (n)curses function has it's counterpart with a more or less similar formal parameter list in the binding. It is not one-to-one with respect to the datatypes. I tried to make records out of the flat chtype and similar structures, so you don't have to do bit operations to mark an attributed character as bold. Just make the boolean member bold of the record true. The binding also hides the structures like WINDOW, PANEL, MENU, FORM etc. ! It's a pure functional API.
• I try to do as much error checking as possible and feasible in the binding. I will raise an Ada exception when something went wrong in the low-level curses. This has the effect that - at least first time in my life - (n)curses programs have now a very rigid error checking, but - thanks to Ada - you don't have to code the orgiastic error checking style of C.
• Support for wide characters is currently not in the binding, as it is not really in ncurses at this point in time.

Limitations

• I provide no SCREEN datatype and functions to set a new screen. If you need this (mostly for debugging I guess), write a small C routine doing all this and import it into your Ada program.
• I provide no functions to switch on/off curses tracing options. Same suggestion as above.
• Although Ada95 is an OO Language, this binding doesn't provide an OO abstraction of the (n)curses functionality. As mentioned above it's a thin binding for the (n)curses functions. But without any doubt it would be nice to build on top of this an OO abstraction of (n)curses functionality.
  The only exception is the method how fieldtypes are represented in this Binding. We provide an abstract tagged type Field_Type from which the various fieldtypes are derived.
• I currently do not support the link_fieldtype functionality of the forms subsystem.
• The *_IO packages are currently output only.

Hierarchy of packages

• Terminal_Interface
  • Curses
    • Mouse
    • Panels
      • User_Data
    • Menus
      • Menu_User_Data
      • Item_User_Data
    • Forms
      • Form_User_Data
      • Field_User_Data
      • Field_Types
        • Alpha
        • AlphaNumeric
        • IntField
        • Numeric
        • RegExp
        • IPV4_Address
        • Enumeration
          • Ada
        • User
          • Choice
    • Text_IO
      • Integer_IO
      • Float_IO
      • Fixed_IO
      • Decimal_IO
      • Modular_IO
      • Enumeration_IO
      • Complex_IO

If you want to navigate through the html pages of the package specs, click here.

Implementation Details

Behind the abstraction

All the new types like Window, Panel, Menu, Form etc. are just opaque representations of the pointers to the corresponding low level (n)curses structures like WINDOW *, PANEL *, MENU * or FORM *. So you can safely pass them to C routines that expect a pointer to one of those structures.

Extended ripoffline() usage

The official documentation of (n)curses says, that the line parameter determines only whether or not exactly one line is stolen from the top or bottom of the screen. So essentially only the sign of the parameter is evaluated. ncurses has internally implemented it in a way, that uses the line parameter also to control the amount of lines to steal. This mechanism is used in the Rip_Off_Lines routine of the binding.

How user defined field types work

TBD

Enumeration fields handling

The (n)curses documentation says, that the String arrays to be passed to an TYPE_ENUM fieldtype must not be automatic variables. This is not true in this binding, because it is internally arranged to safely copy these values.

Using other Ada compilers

This should basically not be a problem.

Port to other curses implementations

Basically it should not be too hard to make all this run on a regular SVr4 implementation of curses. The problems are probably these:

• ncurses has some additional features which are presented in this binding. You have two choices to deal with this:
  • Emulate the feature in this binding
  • Raise an exception for non implemented features

  Most likely you will follow a mixed approach. Some features are easy to simulate, others will be hard if not impossible.

I'm quite sure I forgot something.