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From: Jeff Barnett <jbb@notatt.com>
Newsgroups: comp.theory
Subject: Re: neos Universal Compiler and FORTRAN IV
Date: Fri, 28 Mar 2025 13:05:10 -0600
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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.
-- 
Jeff Barnett