Building on 64-bit Linux

Before attempting the build the project on Linux, the version control repository of the project code was converted from the Concurrent Versioning System (CVS) to git, a more modern version control system. The version installed using Kubuntu's software package manager was 1.7.4.4. However, this version did not have the needed cvs import utility, so the latest version was installed directly from the git repository, though git is required to retrieve it. This was version 1.7.6. Using git will have no impact on this project's software releases except that the CVS versions tags will be removed from the source files.

The intention was to use command line make file distributed with the project to build on Linux. Previously on Windows, NetBeans was used to build the project, though the command line make file (which was initialized generated by an option in NetBeans) was used to test the project before a release. For the moment, NetBeans would not be used (more about this later). Some minor problems needed to be resolved before it would build and work on Linux...

Development Environment Change

Because of a job requirement, I had to install 64-bit Linux on my computer (I chose Kubuntu 10.10, Maverick Meerkat). So development of this project will be moved over to 64-bit Linux, at least for the time being. Since so far, the program only has a simple command line interface (no GUI), this won't cause an immediate problem. The releases will still be tested under Windows XP as I have a Windows XP virtual machine running on Kubuntu. Perhaps when the time comes to start on the GUI, a common tool set will chosen, something like Qt.

For the moment, this will also give the opportunity to present how to set up Windows to be able to build the project since this virtual machine is a new Windows installation and not a clone of my of my previous Windows installation. A lot of things were originally tried and listing the procedure that finally worked in the end was probably impossible.

Also possibly changing will be the actual development tools that will be used. Under consideration is changing the version control system (from cvs to git), the IDE (from NetBeans 6.9.1 to newer version 7.0, which has a plug-in for git, or possibly to the Eclipse CDT IDE), and the build system to build the project (from NetBeans' make system and standalone make file currently distributed with the project to the cmake build system). Each of these will be explained in the posts that follow...

Translator – Colon (Design)

The colon token will work very similar to the end-of-line token and so will have the end statement flag in its table entry. The difference with the end-of-line token is that instead of terminating the translation or a line, the token mode will be set to command for the next statement.

There will be two error conditions. Two colons will not be allowed. While a second colon would not affect anything and is allowed in other BASICs, it will be considered an error here. There is no point to allowing this. Also, a colon will not be allowed at the end of the line with no command after it.

When a colon token is received, the colon sub-code will be set in the command token on top of the command stack. The command token will be appended to the end of the statement when the command has been processed (by the command handler).

However, there is an issue with print statements. The actual print command token may not be appended to the output if there is a semicolon, comma or print function at the end of the print statement. In this case, the print command handler will have to transfer the colon sub-code to the last print code that was appended to the output, which may be a print type (when a semicolon is not needed), comma, semicolon, SPC or TAB.

Colon – Statement Separator

The Colon is used to separate statements in the BASIC language though it is not part of the ANSI BASIC, it is part of the more common BASICs (GW-Basic, QBasic, FreeBasic, etc.). Before moving to the translation of colon tokens, like everything else, the action during run-time must be defined.  However, the Colon does not actually do anything at run-time.

Colons don't actually need to be stored as separately in the program, however, for them to be reproduced, something needs to be put into the internal program. The assumption that there will be a colon at the end of each statement except at the end of the line is not sufficient. Consider this statement:

IF A>B THEN PRINT A ELSE PRINT B:A=B:B=0.0

There is no colon after the first print statement. To reproduce colons properly, there will be a colon sub-code set for a command token that has a colon following the statement. For the statements after the ELSE in the example above, the colon sub-code will be set as shown in this translation:

B PrintDbl'Colon' A<ref> B Assign'Colon' B<ref> 0.0 Assign

When a line is reproduced, the Recreator will add a colon after a statement that has the colon sub-code set.

Translator – A Unary Operator Curiosity

One of the test statements created for testing the unary operator fix was:

A = -B^NOT C% + -D*NOT E%

The intention of this statement was test the NOT unary operator in front of the second operand of both the exponentiation and multiplication operators. The translation of this statement was expected to be (the blue expression being the first operand and the red expression being the second operand of the addition):

A<ref> B C% NOT ^* Neg D Neg E% NOT *%2 + Assign

However, what was produced was this unexpected translation:

A<ref> B C% D Neg E% NOT *%2 +%1 Cvtint NOT ^* Neg Assign

Upon reviewing the precedence of the operators (see Translator – Operator Precedence) and the code, it turns out that this translation was correct. The ADD is higher precedence than the NOT, so the operands of the ADD are C% and the –D*NOT E% expression with MUL (*%2) higher precedence than ADD, its operands are the –D and NOT E%).

So while the exponentiation is highest precedence, with NOT having a low precedence allowed the ADD to bind the rest of the expression to the NOT, which becomes the second operand (yellow above) of the exponentiation, with the first negation being the final operator. In C/C++, the not (!) and negation (-) operators are very high precedence (and there is no exponentiation operator). But here, NOT was given a low precedence just above the other logical operators but below the math operators (see Translator – Operator Precedence for reasoning). Normally the NOT operator would probably not be used in the same expression as exponentiation like above.

Translator – Unary Operator Problem

While testing the negative constant changes, a new problem was discovered with unary operators, specifically this statement:

A = ---B

Which produced a “done stack empty” bug error at the first negation token. The problem occurred because the second negation operator forced the first negation operator from the hold stack because it was greater or equal precedence, and when checking the operand of the first negation operator, there was nothing on the done stack. Here and some additional examples:

A = B*-C
A = B^-C

The first statement translated correctly because negation is higher precedence than multiplication leaving multiplication on the hold stack. However, the second statement failed because negation is lower precedence than exponentiation forcing exponentiation from the hold stack but with only one operand on the done stack generating the done stack empty bug error. A new rule was needed for unary operators.

Basically, unary operators should not force any tokens (unary operators, binary operators, arrays, or functions) from the hold stack regardless of their precedence because not all of their operands have been received yet (the negate and its operand will be their operand and it has not been fully received yet). As currently implemented, other non-unary operators should still force unary operators from the done stack if the unary operator has higher precedence.

The check to force tokens from the hold stack was changed to if the precedence of the operator on the hold stack is higher than the current operator and if the current token is not a unary operator. Unary operators will now not force other tokens from the hold stack, but other tokens will still force unary operators from the hold stack if higher in precedence. While testing this change, a curious result was produced from one of the test statements...

Parser – Negative Constants

Negative constants were previously not considered by the Parser, which interpreted a minus as the subtract operator. The Translator then changed it to a negate operator when it appeared in the operand state. Consider these two examples (along with there current translations):

A = B-1.5      A B 1.5 Sub Assign
A = -1.5+B     A 1.5 Neg B Sub Assign

The reason for the Parser to not look for signs on numerical constants can be seen in the first example. If the Parser produced the four tokens A = B -1.5, the Translator would generate an “expected operator” error at the -1.5 token since a second operand token was received when it was expecting a binary operator. The second example produces an unnecessary negate token after the constant. While perfectly valid, this is not desirable.

In order for the Parser to correctly interpret negative signs on numerical constants, it needs to be aware of whether the Translator is in operand state or not. If in operand state, the Parser can look for a negative sign in front of a number constant, otherwise a minus should be interpreted as an operator.

A new operand state flag was added to the Parser with an access function to set its value (which is initialized to off). The Parser get number routine was modified to have a new sign flag used to determine if a negative sign was found first. This flag will also prevent multiple negative signs. However, it will only check for a negative sign if no digits or a decimal was seen and if the new operand state flag is on.

An access function was added to the Translator to get the current operand state (either operand or operand-or-end state). Before calling the Parser get token routine, the Parser operand state is set from the Translator's current operand state. While testing, a problem was discovered with unary operators...

Parser – Tokens With Parentheses

While correcting issues with define function tokens, it was noticed that it is not necessary to also store the opening parentheses in the string field of the token. This also includes the generic tokens with parentheses. The parentheses is not necessary because there are separate token types to identify tokens with and without parentheses.

It is also advantageous to not store the parentheses so that an array or define function name can be found in the dictionary. For define functions, take the code snippet:

DEF FNHypot(X,Y)
    FNHypot=SQR(X*X+Y*Y)
END DEF
Z = FNHypot(3,4)

Both the FNHypot( and FNHypot tokens appear, which represent the same function. If the parentheses was stored in the dictionary for the function name, it would require complicated string comparisons to figure out that the FNHypot token is the same function. This same issue applies to regular function names.

A similar issue also applies to arrays. When functions and subroutines are implemented, there will be a feature to allow an entire array to be passed to a function or subroutine. Exactly how this will work has not been defined yet, but this code snippet shows how it would look:

DIM Array(10)
CALL subroutine(A)

The changes for removing the parentheses from these tokens were very simple. In the Parser get identifier routine, when creating the string for these tokens, the length provided to the string constructor was changed to be one less than the actual length so the parentheses would not be included. In the Translator when reporting an error at the open parentheses of a define function with parentheses token, the minus one was removed since the length is now one less. Finally, in the token test output routines, an open parentheses was added to the output of these tokens.

Project – Tokens Status Enumeration

Each time a new error (token status) is added, renamed or deleted, two changes were needed. Both the token status enumeration (include file) and the message array (source file) needed to be changed. The correct changes were needed or the two files will be out of sync. To check for problems, code had been added to initialization to check for duplicates and missing entries.

Similar to automatic generation of the code enumeration from the table entries, the token status enumeration will also be generated automatically. Each message array element was a structure containing a token status value and a pointer to a message string. The elements were changed to just the message string with the name of the token status in a comment at the end of the line.

The codes awk script was renamed to enums and was modified to also read the token status message array to generate the token status enumeration automatically be reading the name in the comment after the message string. The name of the output file was changed from codes.h to autoenums.h to be more generic and allow for additional automatic enumerations.

During initialization, in addition to checking for duplicates and missing entries, a translation index array was built to translate from token status value to index. Both the checking and the translation array were removed since they are no longer necessary. The awk script will check for duplicates and the token status is now the same as the index into the message array.

The error type template class is no longer needed for token status errors (but still for the table entry erros). Also, the duplicate and missing were no longer needed and were removed. Some problems were found in this template class for table entries where the range error was not working because the wrong constructor was being called. Instead of storing indexes to the errors, the variables were changed to be the type of the template. This made the range error constructor unique.

Translation – INPUT Command (Release)

The remaining problem was due to the input command handler deleting the token passed in (the token terminating the invalid string prompt expression), however, the caller (the call command handler routine) was also deleting the token since the command handler changed the token to point to the error token. The extra token delete was removed from the input command handler.

The INPUT command is fully working and ibcp_0.1.15-src.zip has been uploaded at Sourceforge IBCP Project along with the binary for the program.  To support the INPUT command, several other changes were needed including making the token codes and table entries indexes one in the same, correcting print function issues, correcting sub-string assignment issues, handling assignment token mode differently, handling define function tokens correctly, implementing an end statement Translator state, and implementing the reference token mode.

Next up, a slight change to the direction of this project to make it a little more interesting. Instead of prodding along with the translation of more commands, work will begin of the other components including the encoder, dictionary, recreator, program (maintaining the internal program and the program editor), and the run-time module.

The goal is to get this BASIC working as there are (almost) enough commands to make a very simple BASIC program (input, assignments and output). Once this is working, more commands can be implemented. But first a couple of minor things will be implemented before proceeding with this new direction.

Translation – INPUT Error Debugging

The main problem with the wrong tokens being reported for errors in the INPUT command was because the token with the error was not put into the command item structure passed to the INPUT command – a requirement of command handlers reporting an error. Once this was added, most of the errors were now pointing to the correct token.

A new “expected operator, semicolon or comma” error was added for when an end statement token (for example the EOL in the incomplete statement INPUT PROMPT A$) is received after a valid string expression because this is a little more accurate than just the “expected semicolon or comma” error.

The two remaining errors were “invalid mode” bug errors that were occurring in the end expression error routine that is called when an end statement token is received during operand state. Support for the reference mode needed to be added to this routine, which needed to return the “expected variable” error.

One problem remains. The error test statement INPUT PROMPT A+B*C is causing extra token deletes, which was detected by the memory leak detection mechanism that was implemented a little while ago. To be continued...

Translation – INPUT PROMPT Debugging

The first problem found with the INPUT PROMPT command was that reference mode was not being set after the string prompt expression was processed. The next problem was that the Translator was still in binary operator state following the comma or semicolon after the string prompt string expression was processed, so this required setting the state back to operand state, which lead to the discovered of some other minor state issues.

The first operand state is very similar to the operand state except that end expression tokens (like comma, semicolon, and EOL) are also acceptable (normally considered operators). This state was implemented for the PRINT command since these tokens are allowed when an operand is expected (for example the PRINT,,A statement). This state is also set after a command is received, and it is up to the command handler to decide if an immediate end expression is allowed (which it currently is only for the PRINT command).

The equal token handler was found to be incorrectly setting the first operand state in an assignment statement. This did not cause a problem because the end expressions operators were being caught elsewhere when in expressions incorrectly (by their respective token handlers). Anyway, calling it the first operand state was a little confusing and was therefore renamed more appropriately to the operand or end state. The equal token handler was corrected to set only operand state.

The valid INPUT PROMPT test statements are now working, now on to the invalid INPUT statements, which for the most part are not reporting the correct token where an error is detected or just not reporting the correct error including some bug errors...

Translation – INPUT Debugging

Several minor issues were found and corrected. When the end of the INPUT command occurs, the last input parse code has to be marked with the end sub-code. Support for reference mode also needed to be added to comma token handler.

When the EOL token was received by the INPUT command handler, it reused the token for the input assign code for the variable. Upon return from command handler, the EOL token handler proceeded to delete the EOL token (which was not the EOL token anymore). To prevent this, a check was added that if the token no longer contains an EOL code, it is assumed to have been used by the command handler and will not be deleted.

The InputBegin code was just being appended to the output, but the first variable had already been added to the output, so it was after the variable instead of at the start of the statement. This code could be inserted at the beginning of the output list, however, this would only work if the INPUT command was at the beginning of the line, which may not be the case (multiple statements per line will be supported).

So instead, the element pointer in the command item will be set to the current last item in the output list when a command is pushed to the command stack. Since this pointer can no longer be checked for null to determine if an input begin code has been added, a new input begin command flag was added, which is set once an input begin code has been added to the output.

Another problem found was that none of the input variables had their reference flag set once added to the output. The find code routine was not checking for a reference (not important) but was clearing the reference flag (a problem) since the token being checked (the input assign code) did not have its reference flag set. The reference flag of the input assign token was set before calling the process final operand routine to make the find code routine work as desired, and then cleared upon return.

The valid INPUT test statements are now working, now on to the INPUT PROMPT statements, which are not working...

INPUT Translation – Variable Handling and Ending

To look up the appropriate input assign code, the process final operand routine is used, which calls the find code routine that checks the token on the done stack to see if the reference flag is set since the input assign codes have the reference flag (this should not be necessary since the INPUT command uses the recently implemented reference mode). The reference variable will be popped from the done stack and the input assign code will be appended to the output before returning.

The InputAssignInt and InputAssignStr are associated codes for the InputAssign code. Once the input assign code has been appended to the output, the appropriate input parse code needs to be inserted after the input begin code or last input parse code. The easiest way to get the appropriate input parse code was to have each (InputParse, InputParseInt, and InputParseStr) be associated codes to the input assign codes. The second associated code will be used for these.

When a final semicolon token is received, the stay on line command flag is set (the same flag used for the PRINT command) and the state is set to end statement. When an end statement token is received, the INPUT command handler check if the stay flag is set and sets the keep sub-code of the INPUT command token, which is then appended to the output.

If an end statement token is received with no semicolon, the INPUT command token is immediately appended to the output without the keep sub-code. The INPUT command handler has now been implemented and the code compiles, so debugging can begin...

Translator – End Statement State

Once a semicolon is received at the end of an INPUT statement, no more tokens should be received except for an end-of-statement token. If another token is received, then an error should be reported. To accomplish this, a new end statement state similar to the end expression state is needed. While the end expression state only needs to be checked when operators are expected, the end statement state needs to be checked for all tokens.

The end statement state check was added just before the check for operand or first operand state in the main translator add token routine. When in end statement state, if the token does not have the end statement flag set in its table entry, then an “expected end-of-statement” error is reported against the token.

The access function for getting the table entry flags for a token already checks if the token has a table entry, and if there is not table entry, then zero (no flags) is returned. Currently only the EOL code has the end statement flag set, but eventually the Colon, ELSE and ENDIF tokens will also and possibly other codes.

Translation – Define Function Token Issues

For now in the process operand routine, define function with parentheses tokens will not be allowed in command or assignment mode. This will need to be changed later when the DEF command is implemented. This check was also made in the check assignment list item routine.

However, since a define function without a parentheses token is allowed in assignments, the error was set to point to the open parentheses as an "expected equal or comma for assignment" error. The open parentheses is at the end of the token, so to get the error to point to it, the column of the token was incremented by the length of the token minus one.

Previously in the close parentheses token handler, the reference flag was being set for token with parentheses and define function with parentheses tokens. This check was modified to only set the reference flag for token with parentheses.

The reference flag for define function without parentheses tokens was already being set, so no change was needed for these tokens.