REQ: Expression parser

REQ: Expression parser

[dagoon]

Hello, I just started coding in ada, so I have problems, esp. with string 
handling since it's much different from C or pascal style... I'd love to 
see an example of expression parser (like getting "2+2" string and giving 
integer=4). I also know that string in ada is saved as (first,last,*text) 
but I don't know if there's any simply method of changing first and last.
thanks for any help, regards
Marcin

Re: REQ: Expression parser

[Dale Stanbrough]

"Hello, I just started coding in ada, so I have problems, esp. with
string 
 handling since it's much different from C or pascal style... I'd love to 
 see an example of expression parser (like getting "2+2" string and
giving 
 integer=4). I also know that string in ada is saved as
(first,last,*text) 
 but I don't know if there's any simply method of changing first and last.
 thanks for any help, regards



Try using the Ada.Strings.Unbounded.Unbounded_String type, this has a very
intuitive set of routines. You can easily build up an i/o package to read
these values in from the user.

Unfortunately it seems some of the more common textbooks seem to overlook
this
very useful type.


Dale

Re: REQ: Expression parser

[Robert Dewar]

dagoon asks

<<Hello, I just started coding in ada, so I have problems, esp. with string
handling since it's much different from C or pascal style... I'd love to
see an example of expression parser (like getting "2+2" string and giving
integer=4). I also know that string in ada is saved as (first,last,*text)
but I don't know if there's any simply method of changing first and last.
thanks for any help, regards
>>

Have a look at Ada.Strings.Unbounded, and no a string in Ada is not
"saved as first,last,*text", it is a more abstract object as you
will see from this specification.

If you want to see some extensive examples of the use of this abstraction,
have a look at the coding of GNAT.Spitbol.Patterns in the GNAT library.