Re: What makes a compiler, was Is Assembler

"cr88192" <cr88192@hotmail.com> wrote in message
> "Tony" <tony@my.net> wrote
>> "Hans Aberg" <haberg_20080406@math.su.se> wrote in message
>>> marco.m.petersen@gmail.com wrote:
>>>> I mean, if you wrote a program that converts code from BASIC to C++
>>>> then calls another compiler to do the compilation process, wouldn't
>>>> that be considered as a compiler?
>>>
>>> Yes, formally a compiler just translates one computer language into
>>> another. For example, an assembler translates into the machine code
>>> language.


>> I would say that is simply translation and not compilation because
>> there is no intermediate representation. The IR (and the creation
>> of it via lex/parse/semantic analysis before code generation) is
>> what I think distinguishes compilers from interpreters and
>> translators.


> I will disagree here...
>
> it is not an IR which makes it a compiler, and infact many simpler
> compilers for many languages may lack an IR altogether...
>
> rather, I think it is more about the semantic symmetry between the
> input and the output. a translator will usually translate between one
> form and another, where both forms represent more or less the same
> semantics, and can be translated between one and the other with little
> or no loss of information (a translator then bases its operation
> primarily on the input and output, converting from one form into
> another, with the internal machinery of the translator being of
> minimal significance).
>
> so, for example, an assembler can convert ASM to machine code, and a
> disassembler can (more or less), get it back...
>
>
> compilers are typically far less symmetric, where what a compiler
> produces can typically not be converted back into what it came from,
> and usually there is a strong divergence in terms of the semantics
> between the input and output (the relation being not so much based on
> the relative structure of the input and output, rather it is based on
> the internals of the compiler itself...).
>
>
> but, many tools may fall into a gray area between these extremes.


A parse tree or AST can be the IR. The IR doesn't have to be something in
between the AST and code generation.


Tony

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