Translator – Table Entry Restructuring

In looking ahead in the design of the assignment operators, I realized the size of the associated code array will need to increase from 2 to 5. This is due (spoiler alert) because there will be three types of strings internally – more on this when the design of strings begins shortly. Having an associated code array size of 5 for only two operators is a waste. There's needs to be a little more efficient storage system that doesn't penalize all the table entries for only two entries. Similarly for the operand data type array (now set at a size of 3).

In thinking about this further, only the operators and internal functions require the data type, unary code, number of operands, operand data types, associated codes and perhaps even the precedence. Currently the precedence for commands is obtained from the table entry, but no actual values have been entered yet. The design and implementation of commands is further done the line, so for now, precedence will remain implemented as is.

Anyway, for operators and internal functions, the information mentioned can be put into an expression information structure, for which a pointer to this structure will be put into the table entry. The expression information structure (class) will have a constructor to initialize the members from the constructors arguments and the new operator will be used to allocate the structure. Likewise for the operand data type and associated code arrays – the arrays will be allocated for only the size needed.

Translator – Data Types On Assignments

The assignment operators need a little bit different handling that regular operators because they require reference tokens for the operands being assigned. The reference tokens will have a specific data type and can not be converted between types. Only the value being assigned can be converted to the type of the reference operands. An added complication with the assignment list operators is that they have no set number of reference operands so the number of operands and the operand data types in the table entries will not work, which the match code routine relies on.

To support the assignment operator, the match code routine needs to be modified so that when it sees a reference operand, to only check if the data type matches exactly to the data type in the table entry. The main assignment operator (Assign, which will handle the double data type) will have two associated codes, AssignInt and AssignStr. The second operand for Assign and AssignInt can be converted.

For the assignment list operators, it has already been decided that all of the variables being assigned must be the same data type, in other words, no mixing of doubles and integers – mainly for efficiency during run-time. The match code routine was not designed to handle a variable number of operands for a code. However, the match code routine can be used, at least to check the two operands on top of the done stack, which would be the value being assigned and the last reference operand in the list being assigned.

In the add operator routine, upon returning from the match code routine successfully, it can then check if the operator is an assignment list operator. This can be accomplish with a new assignment list operator flag in the table entry. If this flag is set, then the add routine would proceed to check the rest of the operands on the done stack for the reference flag (which it does now) and check to see if the data type is the same as the assignment list operator returned from the match code routine.

Translator – Data Types (Release)

The remaining minor bugs were found by simply tracing through using the debugger. There are minor differences in the previous test input sets due to the addition of the internal CvtDbl and CvtInt codes. Many test inputs were added for the sixth set of the test inputs for the data type handling including several error tests.

Now that the source tree is under CVS, the full source tree is being released with all the test sub-directory files. All the test output files have also been located in the test sub-directory. In the future, the full source tree will only be release for major releases (which means for the interim releases, only the main project files, current test output files and any new test program source files will be included).

The code now handles data types in expression (but not the assignment operators) and ibcp_0.1.9‑src.zip has been uploaded at Sourceforge IBCP Project along with the binary for the program (which now will run from the Windows command line and without MinGW being installed). Next the data type handling for the assignment operators...

Translator – Data Types (Implementation)

The final implementation of the data type handling was completed except for assignment operators – these will take a little extra processing because of the references (which are not convertible), plus the assignment list operator does not have a fixed number of operands. The assignment operators will be handled later.

The new find_code() function returns a Status enumeration value, either Good upon success or one of the three new error codes for the “excepted <data type>” errors. A reference to the token is passed so that it can be changed to point to the error. I realized that the comma and close parentheses tokens were not being deleted in all cases. There needs to be some sort of memory leak checking added to the program. The new and delete operators can probably be overloaded, so some checking can be added. This is a side-project for another day, but it is needed.

Testing began with the existing Translator test inputs (1 through 5) – some differences were expected (new conversion codes). What follows are some of the changes that were needed as the debugging progressed:

When the operands are being popped off of the done stack (the operand array needs to be filled in reverse order), the reference flags needed to be cleared (no need to check if it is set first), just like was previously being done for operators and internal functions.

When checking the associated codes and a convertible match is found, it is only recorded if no convertible match has been found so far (in other words, find only the first convertible match).

When changing the token to a new associated code, in addition to changing the index in the token, the data type also needed to be set to new code's data type, which might be different than the main code (for example Abs returns Double, but AbsInt returns Integer).

Quite a few of the expressions in the existing test inputs are not working correctly, or worse, causing the program to crash. One test input VAL(STR$("1.23")) was written incorrectly in the first place, which should have been VAL(STR$(1.23)) or STR$(VAL("1.23")), but at least the code properly detected this error.  Debugging continues...

Project Executable Issue Resolved

The cause of the problem why the executable would not run in the Windows (XP) command window was finally identified. During the transition to CVS, it was discovered that the older executables had no problem running in the command window. The problem started with release 0.1.2 (release 0.1.1 worked). Some time was finally spent investigating what changed between 0.1.1 and 0.1.2 to cause this problem.

During the investigation, it was also discovered that the executables require libgcc_s_dw2‑1.dll to run. This library comes with MinGW. The GCC GNU GPL (General Public License) prevents this library from being distributed with executables without also distributing the source code for it – something not desirable. However, there is the linker option “‑static‑libgcc” that will statically link this library into the executable, which is permitted under the GCC GPL, so future executables will be linked this way. VIDE complains about this option upon loading the project indicating libraries should be entered in the project library tab – but it does correctly use this option on linking. This will be left as is for the moment. Unfortunately, this library issue was not the cause of the command window problem.

After further investigation, the problem was determined to be caused by  the transition from the test_parser program to the ibcp program (the test_parser.cpp source file to the ibcp.cpp and test_ibcp.cpp source files). One of the changes made was in the GPL header print function to print the actual name of the executable, not a fixed string. This simply involved printing the first command line argument. Under MSYS, Insight (GDB) and apparently when run from Windows Explorer, this first argument (argv[0]) contains the full path of the program, which was not desired. A string function was used to find the last back-slash in this full path and only print the string that comes after this character.

The problem was that from the command window, only the program name entered is passed as the first argument (the path or the “.exe” is not included unless entered on the command line). In any case, the strrchr() library function used to get a pointer to the last back-slash returned a NULL because a back-slash was not found, and using this NULL caused the crash. The code was corrected to allow for a lack of a path – problem solved.

Translator – Data Type Matching

When determining which code (main or associated) to use from the operand's data types, there can be an exact match, no match or a convertible match. A convertible match can be made to be an exact match when conversion code(s) are added after the operand that doesn't match exactly. An exact match is preferred.

There will be a match routine that will determine the type of match there is between the current operand's data type(s) and a code's required data type(s). In additional to returning the type of match found (exact, none, or convertible), the conversion codes needed for each operand or Null if a particular operand does not need conversion will also be returned.

This match routine will use an table holding the conversion codes for each possible operand (have) data type and required (need) data type pairs. For the pairs where the two data types are the same, the conversion code will be set to the Null code. For the pairs with an Integer or Double vs. a String, the conversion code will be set to an Invalid code. The only pairs with actual conversion codes are the have Integer need Double pair (CvtDbl) and the have Double need Integer pair (CvtInt).

The routine for finding the code for the data types of the operand(s) will be called from both the add operator routine and the internal function routine (after the number of arguments is checked). The operands will be pulled off of the done stack to get their data types. Using the match routine, the operands will be checked against the main code for a data type match. If an exact match is found, then no further action is needed. If a convertible match was found, the main code is saved in case no further exact match is found.

When the main code is not an exact match, each of the associated codes (if any) of the main code table entry are checked for a match. For each, if an exact match is found, then no further action is needed. If a convertible match was found, the associated code is saved in case no further exact match is found.

If a convertible match was found, then the token's code is changed and the conversion codes are inserted into the output list after the operands. If no match was found, then one of three “expected <data type>” errors (one for each data type) will be reported against the first operand with an Invalid code in the conversion codes returned from the match routine.

Translator – Data Type (Table Updates)

Before working on the design of the routines that will handle the matching of the data types and finding the correct code, I decided to make the changes to the table entries for the new operand data type (operand_datatype) array and associated code (assoc_code) array and make sure these compile. The number of arguments member (nargs) was also renamed to the number of operands (noperands). New access functions for these members were added to the Table class.

All the table entries for the operators and internal functions were updated with the new values. The number of operands (previously nargs) for all of the operators were previously set to zero, so these were changed to 1 for the unary or 2 for the binary operators. The data type for many operators were also incorrectly set to None, so these was changed to the appropriate data type.

New entries for all the associated codes were added to the table and their codes were added to the Code enumeration. An entry for the CDBL functions was missing and was added. An entry for a new function FRAC was also added (this function will return the fractional part of a floating point values).

The integer division operator (“\” or IntDiv) is intended to be used with double operands, which will be rounded and converted to integers internally before the division. The operand data types could have been set to the integer data type, but then the CvtInt would always be inserted for both operands.  This operator only has one code and should not be used with integer operands as the regular division should be used, but this will be allowed (CvtDbl will be inserted, but only to be converted back to integers internally).

The Power operator will have three forms, the standard double/double (Power) and integer/integer (PowerInt), but there will also be a double/integer code (PowerMul). The PowerInt will use integer multiplication internally. The idea for the PowerMul code is for it to also use multiplication internally instead of calling the standard C pow() function for speed. However, the pow() function may already have these optimizations, so this may be unnecessary. Some experiments will be needed to determine which is more efficient. The goal is to allow the programmer to use an expression like A^2 instead of A*A and not be penalized by slow execution.

Translator – Associated Codes

Operators and some internal functions allow different operand data types, each will have it's own code (e.g. Add, AddInt, and CatStr), but only one name in the source (e.g. “+”). The Parser will only find the first one in the table since the Parser is only responsible for breaking the source into tokens, not looking at data types and determining appropriate codes. It is the Translator's responsibility to examine and validate the operands of operators and internal functions and to set the token to the appropriate code.

To accomplish this, the first entry in the table (that the Parser finds, the default entry), which for many will be the code that handles the double data type, will contain the other codes associated to the main code. These codes will be put into an associated code array in the table entry.

After obtaining the data types of the operands from the done stack, the Translator will check to see if there is a match to the code by checking the required operand data types in the code's table entry. If there is no match, then each of the associated code table entries will be checked for a match.

In addition to an exact match, there will also be a convertible match. With this type of match, hidden conversion codes can be inserted to obtain the desired data types. The exact match will be preferred so that the correct code is used. For example, if the first exact match or convertible match is used, then for Integer + Integer, the Translator would use the default Add code (for doubles) and add two CvtInt instead of using the preferred AddInt code. Next, how a convertible match will be detected...

Translator – Operand Data Types

Now it has been established that operators and internal functions can be handled the same way, except that the number of arguments (operands) is checked first for internal functions. For internal functions, the number of arguments check also determines which code to use (MID2 vs. MID3, INSTR2 vs. INSTR3, or ASC vs. ASC2).

Each code (operator or internal function) has a return data type, a fixed number of operands and a expected data type for each operand. The word operand will be used instead of argument from now on, which  is more appropriate when applied to operators. Taking the plus operator as an example, which will have three codes (one main and two associated codes):

Add  Double  (2)  Double  Double
AddInt  Integer  (2)  Integer  Integer
CatStr  String  (2)  String  String

The code is listed first along with the return data type. The number of operands is in parentheses followed by the data type of each operand. If there is an add with a double and an integer operand, the Add code will be used with a CvtInt inserted after the integer operand.

The table entries already contain the code and data type values and the number of arguments will be renamed to the number of operands. A new operand data type array needs to be added to the table entries. The size of this array will be set to three since there are currently no planned functions containing more than three arguments. Next, how associated codes will be handled...

Translator – Operators and Internal Functions

Unary operators have one operand. When the translation to RPN of unary operators is compared to the translation of functions with one argument, it can be seen that the translations are the same (one operand followed by the code):

-A  →  A Neg
ABS(A)  →  A Abs

Binary operators have two operands. When the translation to RPN of binary operators is compared to the translation of functions with two arguments, it can be seen that the translations are the same (two operands followed by the code):

A$+B$  →  A$ B$ CatStr
LEFT$(A$,2)  →  A$ 2 Left

There are no tertiary or more operators, but functions with three of more arguments have a similar format except there would be more operands before the code. So, once the source code for operators and internal functions are translated to RPN, there is no difference between them - operand(s) followed by a code. Therefore, for data type handling, both operators and functions can be handled the same way. Next, how data types will be handled...

Translator – Data Types and Internal Functions

The internal functions have a fixed number of arguments, though some functions have multiple forms with different number of arguments (MID$, INSTR and ASC). Each argument has a specific data type expected, however, integer and double data types are interchangeable as the necessary conversion will be perform like for operators.

Most of the math functions (e.g. INT, SQR, LOG, COS, etc.) have one argument, which is expected to be a double. These functions return a double. Only one code is required for these functions. If the argument is an integer, then a hidden CvtDbl code will be inserted after the integer operand. Here are some RPN examples of math functions:

A Sqr
B% CvtDbl Log

A few of the math functions (ABS and SGN), will return the same type as there operand. Two codes are required for these functions: Abs, AbsInt, Sgn, and SgnInt. The reason for having two codes is so that these functions can be used in integer expressions without any wasteful conversions to and from double precision. This is not necessary for the other math function because they will be calculated in double precision internally.

The conversion functions (CDBL and CINT) return the opposite date type as their operand. These functions work the same is the hidden CvtDbl and CvtInt codes. It would appear that these functions are unnecessary since the hidden conversion codes will be inserted as needed. However, they may be reasons where they are necessary like in function and subroutine calls.

The string functions deal with the string data type (implementation will be delayed along with the string data). Some string functions take an integer operand (CHR$ and SPACE$) or double operand (STR$) and produce a string, some take a string operand and produce an integer (ASC and LEN) or double (VAL), and some take both string and integer operands and produce a string (LEFT$, MID$, RIGHT$, and REPEAT$) or an integer (ASC and INSTR).

Next, the similarity between operators and internal functions...

Translator – Data Types and Operators

Three data types are currently planned: double precision (the default), integers and strings. Several operators accept all three as operands (plus, equality, relational and assignment). Consider the different possible operand combinations for the plus operator (the default data type is double, % is for integers and $ is for strings):

A + B
A + J%
I% + B
I% + J%
S$ + T$

Any combination between a number and a string is invalid and an error needs to be reported. However, doubles and integers may be mixed in an expression. The expression will remain integer for efficiency as long as there are integer operands. In a double expression, integers will be promoted (converted) to double.

If the plus operator was implemented as a single routine, at run-time it would have to look at the operands and then decide what action to take, whether to add two doubles, whether to convert one operand or the other from integer to double and then add two doubles, whether to add two integers, or whether to concatenate two strings. All this decision making will slow execution.

These decisions will of course be made before run-time by the Translator. The Translator will know which operation will be needed at run-time, so it will add the appropriate code to the RPN list. Since there are five different possible combinations, that would mean five different add operator codes. If this same thing was implemented for every operator, then the number of codes and the number of execution routines would be excessive.

There are really only three operations, adding doubles, adding integers and concatenating strings. For the other two combinations, one or the other operand needs to be converted from integer to double. To accomplish this, there will be special hidden conversion codes (which have already been mentioned in several earlier posts). With these hidden codes, the above expressions would be converted to RPN as:

A B Add
A J% CvtDbl Add
I% CvtDbl B Add
I% J% AddInt
S$ T$ CatStr

The Add handles doubles, AddInt handles integers, and CatStr (concatenate) handles strings. The CvtDbl code converts it's integer operand to double. For now, the focus will be on doubles and integers; strings require more involved handling and will be added later. Next, data types and internal functions...

Project – Processes and Insights

The transition to CVS is almost complete (two releases remaining to be put into the repository). While it would have been far simpler just to throw to whole project into CVS as is, I wanted the complete history for each release in the CVS repository as if CVS had been used from the beginning. So this would be a good time to give some insight into the development process of this project.


Most days there is only an hour or two to work of this project either on the code or write blog entries, more on the weekends, sometimes less depending on the demands of my full time paying job and my family. The is an attempt to post at least once a day on what is being worked on or on the design of upcoming components, but some days the code is being worked on and there is no time left to write and proofread a post. Sometimes several entries are written at a time (because there is too much for one post), but wait to post each entry to give some time to work on the code.

The design is ongoing, and is actually being worked on ahead of what is being worked on in the actual code. A lot of notes were made on the design almost six months prior to the first post last December, when the decision was made to actually write code and document the effort in a blog. Many of these notes (like on the Recreator design) have yet to be put to code. It is very helpful to explain the design and the reasons behind decisions in the posts. Many problems are identified during this process. The design notes for future components continue to be made (now in a bound notebook instead of loose pieces of paper).

The parallel development (code and future design) process is the reason why there are few major changes to what has been developed so far. This will be become even more evident when commands are implemented in the Translator. Thought needs to be given to how the command will be executed at run-time, the format of the command when it is encoded into the internal code, and what is needed to recreate the source code from the internal code for editing. Now back to the CVS transition and on to data type handling...

Translator – Assignments (Release)

The test code was modified to output “<ref>” after tokens that have the reference flag set. For the third set of test inputs used for testing arrays and function, there are some differences because the reference flag is now set for array subscripts and function arguments. The unexpected comma error was also changed (replaced with separate unexpected comma errors). For the assignment statement test inputs (fifth set), a lot of different statements were needed to test the many situations that can occur. Many have already been discussed. As bugs were discovered, new test statements were added. There are 9 new possible assignment related errors, so there are statements for each of these.

Some more comma related bugs were discovered, including assigning an multiple dimension array element as in the statement “A(B,C)=D” added an assign list operator instead of an assign operator; and the statement “A(B+C,D=E)=F” generated an error. The bottom line was that the counter stack not empty check also needed to be added to the comma operator code. This resulted in new error “unexpected comma in parentheses” being added.

I'm changing the way the changes made to the code are dated. Previously, all the dates were changed to the date of the release – like all these changes were made the same day, which may not have been the case. The changes are becoming rather involved over many days and this method is not efficient. From this release on, the date will be when the changes are actually made. The time stamp of the file may be more recent because of going back and editing the change history at the top of the file.

I have also decided to put this project under software version control, specifically CVS – with the next release. I have working knowledge of CVS and I discovered that either MSYS came with it, or I installed an MSYS/CVS package. The current version numbers in the source files will be removed and replaced with the CVS revision ID tag. These versions were my attempt at version control anyway. Maintaining all the difference versions as zip files and directories is also not efficient.

The code now handles assignment statements and ibcp_0.1.8-src.zip has been uploaded at Sourceforge IBCP Project along with the binary for the program. The release notes now contain a Planned Roadmap to show upcoming development. Next the handling of data types...

Translator – Assignments and Parentheses

Simply changing the mode to Expression when an open parentheses occurs is insufficient. Statements like “A(B,C)=D” no longer worked correctly because the mode was not set to Command when the equal was processed. Also, statements like “A(B+C)=D” and especially “A(B=C)=D” need to have the mode temporarily set to Expression to process the operators in the subscripts correctly. Simply checking if the counter stack is not empty is sufficient for detecting this situation.  The logic for open parentheses needs to be:

Counter Stack Not Empty: No need to check mode; push open parentheses token on hold stack and push a 0 on the counter stack (which prevents commas).

Command: Return an “unexpected parentheses in command” error. Statements like “(A=B)” and “(A+B)” are not valid.

Equal: Set mode to Expression. This is the start of the expression after an equal (assignment). This will handle statements like “A=(B=3)” and “A=(B)=3” where the expression starts after the open parentheses.

Comma: Return an “unexpected parentheses in assignment list” error. Statements like “A,(B),C=4” are not valid.

Expression: Same as if counter stack is not empty (push token and 0).

When processing a closing parentheses for an open parentheses (not an array or function), the reference flag of the last token added to the output list needs to be cleared. A pointer to this token is on top of the done stack. If this token is an operator like in the expression “(A+B)” then clearing the reference flag has no effect, but in statements like “A=(B)=3” or “A=Function((B),C)” the reference flag of B is cleared.

The counter stack is not empty check also needs to be made when processing operators before checking the mode. In other words, if the counter is not empty, then it is assumed that the Translator is within an expression. This will handle statements like “A(B+C)=D” and “A(B=C)=D” correctly. So this check is needed at both the equal operator section and the no special operator section.  Looks like everything is working correctly, so almost ready to release...

Translator – Assignments (Testing)

While testing comma separated assignment statements, an “unexpected character” error for statements like “A,B,C=4” was occurring from the Parser. This occurred because the Parser was seeing the line as an immediate command and expected a number for B. The Parser was modified to not return errors for these since these can be valid immediate statements.

Before testing the previous Translator tests that consisted of only expressions (which are not normally valid by themselves and would now cause “unexpected operator” errors), the test code needed to be modified for a special expression test mode that would be set for the first four sets of test expressions only. The Translator start() function was modified to optionally initialize the mode to Expression instead of Command.

The reference flags also need to be cleared for the arguments of internal functions as values are needed during run-time. This does not apply to define or user functions as the arguments are planned to be passed by reference by default. Surrounding a variable with parentheses will override this and pass the variable by value. For array subscripts, values are needed during run-time. Remember that the Translator does not know the difference between arrays and user functions, therefore, the reference flag will be left set for array subscripts along with function arguments. The Encoder can clear the reference flags for array subscripts once an array is identified.

While testing, I realized that the mode needed to be changed to Expression when an open parentheses occurs. Statements like “A=(B=3)” and “A=(B)=3” are single assignments and the second equals are the equality operator.  Testing continues...