Documentation for Code-Compiler for Cobol version 0.01


The version 0.01 Cobol compiler was designed to take a cobol source program and translate it into
source code which would compile using the FreeBasic compiler.  It is designed to accept a limited 
subset of the Cobol language for the express purpose of beginning the process of self-hosting a
Cobol compiler, i.e. to allow the Cobol compiler to itself be written in Cobol.  

The program is, for all intents and purposes a "one-shot" compiler; it's designed to allow 
the compiler to generate itself as a program in Basic.  Once the Cobol compiler can translate 
itself, further work with this program will cease as at that point the work will continue 
with the Cobol Compiler source.

At that point the compiler version will be 0.10.  

As this program is just being done to allow the compiler to be developed, it is limited and
has certain requirements for the program submitted to it.

The source file to be read is named "SOURCE.COB".  The output file is named "DEST.BAS".  
These are hard-coded.

The program should be correct.  This is not a full compiler and doesn't do error checking
other than minor tests.  Garbage in will equal garbage out.

ALL keywords MUST BE IN UPPER CASE.

Only 01 levels are permitted in FD 
Only 01 and 05 levels are permitted in Working Storage.  05 Levels must be subordinate to an 01.
Only PIC X and PIC 9 are available.
Define PIC 9 only as 01 level and do not create a subordinate 05 level.
Names used in 01 level and 05 levels must be unique.

Define all quoted literals as an 01 value in working storage, and use the defined name of that
quoted literal in place of a quoted string.  Don't use quoted literals anywhere else.

Spaces may be important in some areas outside quoted strings.  Use care if inserting more than 
one space between items.  Don't put a space immediately before a period.

All paragraphs must begin with a 2 as the paragraph name.

Variables of type Pic 9 will all be type COMP, e.g. integer; size is ignored.  
There is no floating point.

READ and WRITE should be directed to the name on the select statement (select-name).  You can 
use MOVE to transfer data from the identifier in the FD clause to any areas to work on the
information.  Only picture X is supported for READ or WRITE.

Only one statement per line is processed.  Where a statement is an imperative statement for an IF or
READ statement, only one statement following the IF or READ is allowed.

Margin a and b are ignored.  Sequence number is saved for error reporting (if any) and may be blank.
Column 7 * is a comment and is ignored.

Division and section headers aren't needed but may be included.

IDENTIFICATION DIVISION.
Completely optional; Only permitted statement is
    PROGRAM-ID.  identifier.
identifier is saved but not used.    
    
ENVIRONMENT DIVISION.    
These three may be included; they are ignored.
     ENVIRONMENT DIVISION    
     INPUT-OUTPUT SECTION. 
     FILE-CONTROL.

To use a file it must be selected
     SELECT select-name ASSIGN TO "quoted file name". 
     this select name must be referenced by an FD.
     
DATA DIVISION.
The following may be included; they are ignored.
DATA DIVISION.
FILE SECTION.
WORKING-STORAGE SECTION.

A file chosen with select must be defined by FD
FD select-name.
This is immediately followed by an 01 level identifier.
01 file-buffer PIC X(80).
which defines the size of the buffer for the file.  Reads will automatically populate 
this area; writes will automatically write from this area.  This area cannot be subdefined
with 05 level.

Entries in Working Storage are as follows
01  identifier     PIC X(amount) [VALUE 'text'].
or
01 identifier-1.
05 identifier-2  PIC X(amount) [VALUE 'text'].
05 identifier-3  PIC X(amount) [VALUE 'text'].



     
PROCEDURE DIVISION.
The following Procedure Division statements are allowed


   2paragraph-name.             -- Defines start of a paragraph.  Must begin with '2'.
   
   CLOSE select-name.           -- Close open file
   DISPLAY identifier.          -- Print message on console
   IF
   MOVE
   OPEN INPUT select-name.      -- Open a file for reading
   OPEN OUTPUT select-name.     -- create a file for writing
   PERFORM paragraph-name       
   PERFORM paragraph-name UNTIL condition.
   READ                         -- read from an open file
   STOP RUN.                    -- end program
   WRITE select-name.           -- write to an output file
   

If statement is of form
     IF condition
        statement.
   or
     IF [NOT] AT END select-name
        statement.
        
   Condition is 
      identifier = | <> | < | > identifier
      
      
MOVE identifier-1 [identifier-2 [identifier-3]] TO identifier-target.

     If identifier-2 is specified, it is concatenated to the end of identifier-1.
     if Identifier-3 is specified, it is concatenated to the end of identifier-2.
     
READ statement is of form
     READ select-name.
    or
     READ select-name AT END
        statement.