Re: Float -> String conversion?

[gauthier@alphainfo.unilim.fr (Michel Gauthier)]

In article <5lbj80$k4p$1@goanna.cs.rmit.edu.au>, Dale Stanbrough
<dale@goanna.cs.rmit.EDU.AU> wrote:

>>  There are two ways that i know of that you can convert from a float
>>  to a string.
>>  
>>          Float'image  - which is in x.xxxxExx format
>>          Ada.Float_Text_IO.Put
>>  
>>  ...but Text_IO is a rather large beast, and many people say
>>  that 'no one ever really uses text_io for _real_ work'.
>>  
>>  If this is the case, then how could one portably convert a float
>>  to a string?

I agree with the idea that Ada.text_IO is harmful :
 - device-dependent,
 - didactically obsolete,
 - mixing of disk keeping and user interface.
 - using disk files implies opening 'standard' files.

To work around the problem, I systematically add to all value
(number-like) types a package for string<-> value conversion
(the specification mimics predefined attributes and Text_IO
subprograms) :

generic

    type ITEM_TYPE is digits <> ;

package STRINGS_FOR_FLOAT is

    function WIDTH return POSITIVE ;
    function IMAGE ( FROM : ITEM_TYPE ) return STRING ;
    function VALUE ( FROM : STRING ) return ITEM_TYPE ;
    procedure PUT ( TO   :     out STRING    ;
                    ITEM : in      ITEM_TYPE ) ;
    procedure GET ( FROM : in      STRING    ;
                    ITEM :     out ITEM_TYPE ;
                    LAST :     out POSITIVE  ) ;

end STRINGS_FOR_FLOAT ;

and a package for request-to-user operations :

generic

    type FLOAT_TYPE is digits <> ;

package REQUESTS . FOR_FLOAT is

    function REQUEST_A_FLOAT
              ( PROMPT      : STRING ) return FLOAT_TYPE ;

    function REQUEST_A_FLOAT
              ( LOWER_BOUND : FLOAT_TYPE ;
                UPPER_BOUND : FLOAT_TYPE ;
                PROMPT      : STRING ) return FLOAT_TYPE ;

    function REQUEST_A_FLOAT
              ( PROMPT      : STRING ;
                EMPTY_LINE  : FLOAT_TYPE ) return FLOAT_TYPE ;

    function REQUEST_A_FLOAT
              ( LOWER_BOUND : FLOAT_TYPE ;
                UPPER_BOUND : FLOAT_TYPE ;
                PROMPT      : STRING ;
                EMPTY_LINE  : FLOAT_TYPE ) return FLOAT_TYPE ;

    generic
        with function CONTROL ( APPLIED_TO : FLOAT_TYPE ) return BOOLEAN ;
        CONTROL_MESSAGE : STRING ;
    function REQUEST_A_FLOAT_WITHOUT_DEFAULT
              ( LOWER_BOUND : FLOAT_TYPE := FLOAT_TYPE ' FIRST ;
                UPPER_BOUND : FLOAT_TYPE := FLOAT_TYPE ' LAST ;
                PROMPT      : STRING ) return FLOAT_TYPE ;

    generic
        with function CONTROL ( APPLIED_TO : FLOAT_TYPE ) return BOOLEAN ;
        CONTROL_MESSAGE : STRING ;
    function REQUEST_A_FLOAT_WITH_DEFAULT
              ( LOWER_BOUND : FLOAT_TYPE := FLOAT_TYPE ' FIRST ;
                UPPER_BOUND : FLOAT_TYPE := FLOAT_TYPE ' LAST ;
                PROMPT      : STRING ;
                EMPTY_LINE  : FLOAT_TYPE ) return FLOAT_TYPE ;

end REQUESTS . FOR_FLOAT ;

I planned also an any-device specification, but could not find time to
complete coding it.

I have similar packages for all classes of predefined numeric types, and for
calendars, polynomials, sets,...  (Requests is often a child of *.Strings in
a generic context)

Both specifications do not depend on Ada.Text_IO and are 
device-independent. Any relevant body can be coded, notably
Requests for window-systems or Strings with different image or parser.

Additionally, it would be useful to have a package containing only the
part of Text_IO with File_Type parameters and no predefined 'file'.

Hope this helps. Any comment appreciated.

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