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From: Jeff Barnett <jbb@notatt.com>
Newsgroups: comp.theory
Subject: Re: neos Universal Compiler and FORTRAN IV
Date: Sat, 29 Mar 2025 00:22:08 -0600
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On 3/28/2025 1:27 PM, Mr Flibble wrote:
> On Fri, 28 Mar 2025 13:05:10 -0600, Jeff Barnett wrote:
> 
>> On 3/28/2025 8:14 AM, Mr Flibble wrote:
>>> On Fri, 28 Mar 2025 14:01:40 +0200, Mikko wrote:
>>>
>>>> On 2025-03-19 16:11:18 +0000, Mikko said:
>>>>
>>>>> On 2025-03-19 14:32:30 +0000, Mr Flibble said:
>>>>>
>>>>>> On Wed, 19 Mar 2025 12:26:20 +0200, Mikko wrote:
>>>>>>
>>>>>>> On 2025-03-18 14:08:50 +0000, Mr Flibble said:
>>>>>>>
>>>>>>>> On Tue, 18 Mar 2025 15:59:45 +0200, Mikko wrote:
>>>>>>>>
>>>>>>>>> On 2025-03-17 16:53:01 +0000, Mr Flibble said:
>>>>>>>>>
>>>>>>>>>> On Mon, 17 Mar 2025 11:21:05 +0200, Mikko wrote:
>>>>>>>>>>
>>>>>>>>>>> On 2025-03-16 18:40:42 +0000, Mr Flibble said:
>>>>>>>>>>>
>>>>>>>>>>>> On Sun, 16 Mar 2025 12:28:24 +0200, Mikko wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> On 2025-03-15 15:08:47 +0000, Mr Flibble said:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Sat, 15 Mar 2025 11:55:52 +0200, Mikko wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On 2025-03-15 04:00:52 +0000, Mr Flibble said:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Hi!
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> neos universal compiler (that can compile any programming
>>>>>>>>>>>>>>>> language)
>>>>>>>>>>>>>>>> is successfully running the tokenization stage tokenizing
>>>>>>>>>>>>>>>> a program written in the neos reference language. #cpp
>>>>>>>>>>>>>>>> #coding #compiler #compsci #gamedev
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> /Flibble
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Can it tokenize FORTRAN 60 or FORTRAN IV ?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> ANY programming language.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> /Flibble
>>>>>>>>>>>>>
>>>>>>>>>>>>> How is neos configured to tokenize FORTRAN 60 ?
>>>>>>>>>>>>
>>>>>>>>>>>> The same way you would configure it for any other programming
>>>>>>>>>>>> language.
>>>>>>>>>>>
>>>>>>>>>>> If it is configured the same for each programming language then
>>>>>>>>>>> how does it know how to tokenize?
>>>>>>>>>>
>>>>>>>>>> You configure it by providing a language specific neosBNF schema
>>>>>>>>>> (grammar)
>>>>>>>>>> file (an input to the compilalation process).
>>>>>>>>>
>>>>>>>>> Is there a neosBNF schema that describes the tokens of FORtRAN 66
>>>>>>>>> or Algol 60?
>>>>>>>>
>>>>>>>> Not yet.
>>>>>>>
>>>>>>> The definition of string literal of Algol 60 would be a good
>>>>>>> example of something that cannot be defined with a regular
>>>>>>> expression and is therefore impossible or at least complicated with
>>>>>>> an ordinary tokenizer.
>>>>>>
>>>>>> neos does not use regular expressions and the neos grammar is
>>>>>> context sensitive (i.e. not context free).
>>>>>
>>>>> A context free grammar should be enough for tokenizing strings of
>>>>> Algol 60.
>>>>>
>>>>> Tokenizing statements of FORTRAN 66 is a harder problem.
>>>>
>>>> Some test cases for a FORTRAN IV tokenizer:
>>>>
>>>>           REALITY IS, AS I MAY LOGICALLY SAY, REAL LOGICAL = WHAT I SAY
>>>>
>>>> Note that these lines begin with 8 spaces.
>>>>
>>>> Tokens on the first line:
>>>> keyword REAL identifier ITYIS comma identifier ASIMAY end of statement
>>>>
>>>> Tokens on the second line:
>>>> keyword LOGICAL identifier LYSAY comma identifier REAL end of
>>>> statement
>>>>
>>>> Tokens on the third line:
>>>> identifier LOGICAL assignment symbol identifier WHAT I SAY
>>>>
>>>> Parser needs to know whether an instance of REAL or LOGICAL is an
>>>> identifier or keyword.
>>>>
>>>> I don't understand how neos can be configred to tokenize the above
>>>> test lines and other FORTRAN IV statements.
>>>
>>> If a native FORTRAN IV compiler can parse it then neos can parse it as
>>> long as it is somehow expressable in the neos attribute grammar.
>>
>> But that was the question: Can it be parsed in a neos expressible
>> grammar? Note that those early Fortran grammars were 1) not finite
>> state, 2) not context free, and 3) inherently ambiguous.It was possible,
>> for example, to write a "format" and an "assignment" statement that were
>> character to character identical. As an aside, a friend who wrote an
>> early Fortran compiler that compiled such a chimera so that it would do
>> an assignment if executed and could be referenced as a format from an IO
>> statement.
> 
> The tokenisation step is entirely optional in neos which instead deploys a
> configurable multi-stage parsing "pipeline" so again there should be no
> problem if FORTRAN IV is expressable in the neos attribute grammar given
> the problem is itself not intractable as FORTRAN IV compilers already
> exist.

I REPEAT -- But that was the question: Can it be parsed in a neos 
expressible grammar?
-- 
Jeff Barnett