1. A General File Interface for Programme INVERSE

The file interpreter functions of the interface enable searching for specific data in the interface files, reading data from these files, writing data to these files, controlling and influencing the state of these files, and controlling the interface system. The expression evaluator’s functions of the interface enable getting information about the interface system and the interface files.

The interpreter functions which perform searching, reading and controlling the state of the interface files are divided into two groups. The first group of functions perform these operations on the pre-defined file infile, and the other group of analogous functions perform analogous operations on arbitrary files defined during the programme runtime. Such division is introduced because of greater simplicity. The user should not have problems by remembering the names and syntax of both groups of functions because each function from one set has an analogous function with similar name and syntax in the other. Functions from the second group have a sub-string “file” instead of “f” in their names (e.g. filefindstring instead of ffindstring) and have an additional argument - the specification of the file on which they operate. This additional argument is always the first one in the function’s argument block and the other arguments are identical.

Functions which read the data, search for different items or write data to files always operate from the current position of the file, so the starting point of the operation does not have to be specified. After the operation is completed, the current position of the file is set to the most logical point according to the kind of operation. For the functions which read or write data such point is after the last read or written byte. There are in general two kinds of functions which search for data items. Functions of the first kind set the current position after a successfully performed operation to the position of the first byte of the found item while the functions of the second kind set the position to the first byte after the found item. There are exceptions to this rule. Functions ffindbrac and filefindbrac which search for closed pairs of brackets set the current position to the first byte after the opening bracket if there are any characters between the opening and the closing bracket, and to the first character after the closing bracket if it follows immediately the opening bracket. Such behaviour is logical because it is expected that the operations on the file which will follow a search for a closed pair of bracket will start inside the bracket pair anything is contained in the brackets, otherwise these operations will start after the brackets. An error code is also recorded if the found brackets contain nothing since this is often an unexpected situation.

The described arrangement simplifies working with the interface and enables the user to use as few intermediate variables as possible. However, in many cases it does not suffice for exchanging data through files. Sometimes we need to jump to arbitrary positions which are somehow connected to operations which were previously performed on a file. A special set of functions was created to enable this by remembering and setting the current position in a specific file. The expression evaluator’s functions getfpos and getfilepos return the current position of a file. The file interpreter functions fmarkpos and filemarkpos assign the current position of a file to the expression evaluator’s variable the name of which is specified in the argument block of the corresponding function. The file interpreter functions fsetpos and filesetpos set the current position of a file to the value specified in the argument block of the corresponding function. Sometimes the functions fincreasepos and fileincreasepos which increase or decrease the file position are more appropriate.

Another mechanism of remembering characteristic positions during the interfacing operations is available. Most of the functions for reading and writing allow the user to call them with additional arguments which specify the names of variables of the expression evaluator to which the characteristic positions of the corresponding operations. For example, in the argument blocks of the functions ffindbrac, fskipbrac, filefindbrac and fieskipbrac the user can optionally specify names of the expression evaluator’s variables to which the position of the found opening and closing bracket are assigned, respectively. If only one name is specified, the position of opening bracket is assigned to the appropriate variable.

In general, in functions which search for different items, the user can additionally specify at most two names of expression evaluator’s variables for marking characteristic positions. At functions which set the current position in the file to the beginning of the found item, the position of the found item is assigned to the first variable and the position of the first byte after the found item is set to the second variable. It is other way around at the functions which set the position after the found item. Only one instead of two variable names can also be specified. Functions for finding closed pairs of brackets have more specific behaviour (see above). At functions which search for characters only one additional variable name can be specified in their argument blocks (two would not make sense because a character has a constant length 1). The current position after a successfully performed operation is assigned to the corresponding variable.

If the appropriate operations are not performed successfully, unusual values are assigned to variables determined by additional arguments for marking characteristic positions of the operations. Values lesser than 1 which can not represent file positions are usually used for this purpose. Therefore, the user can also test if operations were performed successfully through the values of these auxiliary variables. The same is not valid for functions which perform reading and writing.

At the functions which read data, two additional arguments for marking characteristic file positions of the appropriate operations are allowed in their argument blocks. The current position in the file before the beginning of the operation is assigned to the expression evaluator’s variable corresponding to the first additional argument, and the position of the first byte of the last piece of data which was read is assigned to the variable corresponding to the second additional argument.

The functions for searching and reading have the corresponding analogous functions which perform the same operations in a limited range in files. Such analogous functions have similar names with a suffix “to”. They also require one additional argument which specifies the end of their range of action (the beginning is determined by the current position in the file, as usual). This is the first argument at functions which operate on the pre-defined file infile and the second at functions which operate on arbitrary files (the file specification is the first argument at such functions).

The general file system has a special way of handling errors. Normally all file interpreter and expression evaluator’s functions of the optimization notify the user about errors by writing error reports to the standard output and to the shell’s output file. At the interface we have a specific situation that a failure of an operation may or may not mean an error, dependent on the situation. This is especially expressive at searching operations. Typically, when we search for specific data in a file which contains various data written according to some rules, a lot of failed search operations are performed. This does not indicate that some data is missing, but only gives us additional information which we need in order to locate the data.

Because only true erroneous situations should be reported as errors, there should be a possibility of distinguishing between expected and unexpected failures of operations. A mechanism which enable this is built into the interface system. Failures which do not necessarily mean errors are not reported automatically, but are registered so that they can be examined after the operation is completed. A decision can then be brought whether the failure means an error or not. An error report can then be written only in the case that the failure of the operation means an error, otherwise further actions are undertaken normally. Unexpected situations which are definitely errors are not treated in an usual manner so that error reports are immediately written to the standard output and the output file of the shell.

There are two mechanisms of recording failures which are not automatically reported as errors. File interpreter functions save their status of success which is a zero integer if the function was performed successfully or a non-zero integer if the function failed in any sense. The programme keeps only one code of success so that it is overwritten by the next executed interface function. The user can obtain the value of this code by the expression evaluator’s function fileoperror called without arguments, and so check if the last operation was performed successfully. The file interpreter functions printfileoperror and fprintfileoperror can be used to print a report about the success status of the last operation of the general file interface. These functions must also be called without arguments to write such report.

Beside keeping in memory the success code of the last performed operation of the general file interface, at all instances of failures the appropriate codes are pushed to a special stack. These codes are the same as the above mentioned success codes, the only difference is that code zero which identifies successful operation is not pushed on the stack. The user can retrieve information about these codes by the same functions as for getting information about the success codes of the last performed operation, only that in this case the error must be specified by the position on the stack of errors.

If the function fileoperror is called by argument 0, the number of errors on the stack is returned. If it is called by a positive number, the appropriate error is returned where the argument identifies the successive number of the error code on the stack. If the argument is negative, its absolute value identifies the successive number of the error on the stack counted backwards. If the value of the argument exceeds the number of errors on the stack, zero is returned.

The meaning of the argument at the functions printfileoperror and fprintfileoperror is similar, except that when the argument is zero, a report about all errors is printed, which is also the case if the argument is greater by absolute value than the number of errors.

The number of errors that can be stored on the error stack is limited. When the limit is exceeded, the first few errors are cleared. The user can make the programme report every occurance of this situation by the reportfileoperrorexcess function called by a non-zero argument.

1.3 Some General File Interpreter Functions of the Interface

1.3.1 Controlling the Interface System

1.3.1.1 reportfileoperrorexcess { <switch> }

Specifies wether or not writing reports when a few file operation errors are cleared due to the excess of maximum allowed number of errors on the error stack. If switch is non-zero, the programme will report when cuch situations will occur, otherwise it will not.

1.3.1.2 fprintfileoperror { <num> }

Prints a report about a specific error or errors which have occurred during the file operations, to the optimization shell's output file.

If the function is called without arguments, it prints the report about error status of the last file operation. Each file operation records its error status. This is a code of the last error which occurred during the operation and is not automatically printed to standard output or the shell's output file. These are normally used to indicate situations which don't necessarily mean unexpected behaviour, for example if a string which is searched for in a file is not found. In some situations this can be absolutely normal, therefore the appropriate function of the shell will not automatically report an error, but the user can still check if such situation has occurred, because in some occasions this can mean that something had gone wrong.

Code zero indicates that no error has occurred during this operation. An error status of the next file operation overwrites the error status, but the information about an error is not lost since non-zero error codes are pushed to a stack from which they can be retrieved and appropriate error messages can be printed. This is done by functions printfileoperror and fprintfileoperror when they are called with an argument (num) which specifies a number of error on the stack.

num can be specified in any standard way in which numbers are specified in argument blocks of commands (as a number, as an expression or as a variable in the system of the expression evaluator). If the value of num is zero, error message for all recorded error codes are printed to the output file. If it is a positive number not greater than the number of recorded error codes, a message for the num-th error is printed to the output file (if it is greater than the number of recorded errors, then error messages for all errors are printed). If the value of num is negative and its absolute value is not greater than the number of recorded error codes, then an error message for the num-th error code, counted from the end of the stack, is printed (again a report about all recorded error codes is printed if -num is greater than the number of recorded errors).

All error codes of the file operations can be cleared from the stack by the clearfileoperrors function. The user can so keep trace only about errors which occur from a specific point on.

It is good to know that the number of error codes which are remembered is limited. When the number of recorded error codes execs a specific pre-defined value, the first few errors are cleared from the stack.

1.3.1.3 printfileoperror { <num> }

Prints a report about a specific error or errors which have occurred during the file operations, to the standard output. Otherwise this function is identical to fprintfileoperror.

1.3.1.4 dprintfileoperror { <num> }

Prints a report about a specific error or errors which have occurred during the file operations, to the standard output and the programme’s output file. Otherwise this function is identical to fprintfileoperror.

1.3.1.5 fwritefileoperror { <num> }

Prints an error string which corresponds to a specific error or errors which have occurred during the file operations, to the programme’s output file. The meaning of optional argument num is the same as at function fprintfileoperror.

1.3.1.6 writefileoperror { <num> }

Prints an error string which corresponds to a specific error or errors which have occurred during the file operations, to the standard output. Otherwise this function is identical to fwritefileoperror.

1.3.1.7 dwritefileoperror { <num> }

Prints an error string which corresponds to a specific error or errors which have occurred during the file operations, to the standard output and the programme’s output file.. Otherwise this function is identical to fwritefileoperror.

1.3.1.8 clearfileoperrors { }

This function clear all error codes from the stack of file operation error codes and also sets the error code of the last file operation to zero. It is used to record all file operation errors anew from a specific point.

1.3.1.9 setfileopbuflength { length }

Sets the size of the buffer which is used ad searching operations to length. The default buffer length is 200 bytes and can be changed at any time. It is ideal if the buffer length is of the same magnitude of order than the expected search length since in this case only one or a few reading operations will be performed to find what is searched for. This is good because accessing input-output devices is usually time consumable. On the other hand, it is not good if the buffer is much larger than the expected search length because in this case a lot of necessary data will be read from the file which is also time consuming. If the expected search length is extremely large, i.e. takes a significant portion of memory available on the system, the buffer length must be smaller than recommended above because in the opposite case we can have problems with insufficient memory resources.

1.4 File Interpreter Functions of the Interface which Operate on the Pre-defined File “infile”

1.4.1 Controlling the State of the File

1.4.1.1 fprintfpos { }

Prints a report about the current position in the file infile to the shell's output file.

1.4.1.2 printfpos { }

Prints a report about the current position in the file infile to the standard output.

1.4.1.3 dprintfpos { }

Prints a report about the current position in the file infile to the standard output and the programme’s output fie.

1.4.1.4 fprintfpart { pos1 <pos2> }

Prints a part of the file infile to the shell's output file. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is printed. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is printed. It prints the file part in the form of a report where it also prints which part of the file is printed.

If both pos1 and pos2 are specified, they can be zero, and pos2 can be greater than the length of the file. In this case, if pos1 is zero, it is changed to 1, if pos2 is zero, it is changed to the length of the file, and if pos2 is greater than the length of the file, it is also changed to the length of the file before the operation is performed. If only pos1 is specified, it must be greater than zero. If in this case pos1 bytes from the current position would exceed the length of the file, pos1 is reduced before the operation so that the length of the file is matched.

An error is recorded if pos1 or pos2 are invalid. If the file variable is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.4.1.5 printfpart { pos1 <pos2> }

Does the same as fprintfpart, except that it prints to standard output.

1.4.1.6 dprintfpart { pos1 <pos2> }

Does the same as fprintfpart, except that it prints to the standard output and to the programme’s output file.

1.4.1.7 fwritefpart { pos1 <pos2> }

Prints a part of the file infile to the shell's output file. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is printed. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is printed. Only the file part is printed without any explanation or newlines, so this function is useful if the user wants to use the contents of a file as a part of the output which he generates on his own way.

An error is recorded if pos1 or pos2 are invalid. If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.4.1.8 writefpart { pos1 <pos2> }

Does the same as fwritefpart, except that it prints to standard output.

1.4.1.9 dwritefpart { pos1 <pos2> }

Does the same as fwritefpart, except that it prints to standard output and the programme’s output file.

1.4.1.10 fsetpos { pos }

Sets the current position in the file infile to the value of pos. pos should be a non-negative number not greater than the file size. If it is not an integer, it is rounded to the nearest integer. If it is zero, it is changed to the length of the file plus 1 before the operation is performed.

If it pos is greater than the length of the file, an error is recorded and the position is set to the end of the file (file length plus 1). If rounded pos is less than zero, an error is recorded and nothing else happens. If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.4.1.11 fincreasepos { inc }

Increases the current position in the file infile by inc. inc is rounded to the nearest integer. It can be negative (in this case the current position is decreased) or zero.

If the new position would be less than 1, an error code is recorded and the current position is set to 1. If the new position would be greater than the file length, an error code is recorded and the current position is set to the end of the file (the length of the file plus 1).

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.4.1.12 fmarkpos { pos }

Marks the current position in the file infile. The position is assigned to the expression evaluator’s variable named pos. If the position can not be determined, an integer value less than 1 is assigned to the variable.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. An error is not reported or recorded if the file is not connected to a physical file. In this case the marked position is less than one.

1.4.1.13 fflush { }

Empties the file buffer of the pre-defined file infile and writes the unsaved data on the disk.

This function is used only in special ocasions, for example when we debug the command file and would like to check the effect of file operations directly by editing a file. by executing the fflush command we make sure that all performed file operations take effect, since files are buffered and many operations only take immediate effect on the buffer, not on the file.

1.4.2 Searching for the Data

1.4.2.1 ffindstring { string <pos after> }

Searches for the string string in the file infile from the current position on. If the string is found, it sets the current position of this file to the first byte of the found string. pos and after are optional arguments which specify the names of expression evaluator's variables into which additional information is stored. The function assigns the position of the string to the variable named pos and the position of the first byte after the string to the variable named after.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the string is not found, an appropriate error code is recorded.

1.4.2.2 ffindstringto {to string <pos after> }

Like ffindstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.3 fskipstring { string <after pos> }

Searches for the string string in the file infile from the current position on. If the string is found, it sets the current position of this file to the first byte after the found string. Optional argument after specifies the name of the expression evaluator's variable to which the function assigns this position, and pos specifies the variable to which this function assigns the position of the found string (i.e. the first byte if this string if the file).

1.4.2.4 fskipstringto { to string <after pos> }

Like fskipstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.5 fmultfindstring { {string1 string2 string3 string4 ...} <which pos after> }

Searches for the first occurrence of any of the strings string1, string2, string3, etc. in the file infile from the current position on. If it finds any of these strings, it sets the current position to the position of the found string. Strings must be in curly brackets.

If argument which is given, the function assigns the ordinary number of the found string to the expression evaluator variable named which. If argument pos is given, the function assigns the position of the found string to the appropriate expression evaluator variable, and if after is also given, the function assign the position of the first byte after the found string to the variable with such name.

1.4.2.6 fmultfindstringto { to {string1 string2 string3 string4 ...} <which pos after> }

Like fmultfindstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.7 fmultskipstring { {string1 string2 string3 string4 ...} <which after pos> }

If argument which is given, the function assigns the ordinary number of the found string to the expression evaluator variable named which. If argument after is given, the function assign the position of the first byte after the found string to the expression evaluator's variable named after, and if pos is also specified, the function assign the position of the found string to the variable with such name.

1.4.2.8 fmultskipstringto { to {string1 string2 string3 string4 ...} <which after pos> }

Like fmultskipstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.9 ffindcharacter { charstring <pos> }

Searches in the file infile from the current position for the first occurrence of a character included in the string charstring. If the search is successful then it sets the current position in the file to the position of the found character.

Optional argument pos specifies a name of the expression evaluator’s variable to which the position of the found character is assigned. If the search is not successful then a number less than 1 is assigned to that variable.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the character is not found, an appropriate error code is recorded.

1.4.2.10 ffindcharacterto { to charstring <pos> }

Like ffindcharacter, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.11 fskipcharacters { charstring <pos> }

Searches in the file infile from the current position for the first occurrence of a character not included in the string charstring. If the search is successful then it sets the current position in the file to the position of the found character.

1.4.2.12 fskipcharactersto { to charstring <pos> }

Like fskipcharacters, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.13 ffindblank { <pos> }

Searches in the file infile from the current position for the first occurrence of a blank character, i.e. space, tab, newline, carriage return or null character. If the search is successful then it sets the current position in the file to the position of the found character.

1.4.2.14 ffindblankto { to <pos> }

Like ffindblank, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.15 fskipblanks { <pos> }

Searches in the file infile from the current position for the first occurrence of a non-blank character (blank characters are the space, tab, newline, carriage return and null character). If the search is successful then it sets the current position in the file to the position of the found character.

1.4.2.16 fskipblanksto { to <pos> }

Like fskipblanks, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.17 fnextline { <pos> }

Sets the current position in the file infile to the beginning of the next line from the current position in this file. If such position is found, it sets the current position in this file to it.

Optional argument pos specifies a name of the expression evaluator’s variable to which the position of the found position is assigned. If the search is not successful then a number less than 1 is assigned to that variable.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the next line can not be located (e.g. when the current position is in the last line of the file), an appropriate error code is recorded.

1.4.2.18 ffindbrac { bracstr <pos1 pos2> }

Searches in the file infile from the current position for the first occurrence of a closed bracket specified by bracstr. The first character of bracstr must be the character used for the opening bracket and the second character of the string must be the character used for the closing bracket. These characters may not be the same. Sequences which represent special characters can be used in this string. If the search is successful then the function sets the current position in the file to the position of the first character inside the bracket if the bracket contain any characters, otherwise it sets the current position to the position of the first character after the bracket.

Optional arguments pos1 and pos2 specify names of the expression evaluator’s variables to which the position of the found opening and closing bracket is assigned. If the search is not successful then a number less than 1 is assigned to those variables.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if a bracket is not found, an appropriate error code is recorded. An error code is also recorded if a bracket is found but does not contain any characters, i.e. the closing bracket immediately follow the opening bracket.

1.4.2.19 ffindbracto { to bracstr <pos1 pos2> }

Like ffindbrac, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.20 fskipbrac { bracstr <pos1 pos2> }

Searches in the file infile from the current position for the first occurrence of a closed bracket specified by bracstr. The first character of bracstr must be the character used for the opening bracket and the second character of the string must be the character used for the closing bracket. These characters may not be the same. Sequences which represent special characters can be used in this string. If the search is successful then the function sets the current position in the to the position of the first character after the bracket.

1.4.2.21 fskipbracto { to bracstr <pos1 pos2> }

Like fskipbrac, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.22 ffindnumber { < start next val > }

Searches in the file infile from the current position for the first occurrence of a string which can represent a number. The number can be written in any standard format in which numbers are written in text files. If a number is found, the current position in the file is set to the position of the first character of the string which represent the number.

Optional arguments start, next and val specify names of the expression evaluator’s variables to which the position of the found number, the position of the first character after the number, and the value of the number are assigned, respectively. If the search is not successful then integer numbers less than 1 are assigned to start and next.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if a number is not found, an appropriate error code is recorded.

1.4.2.23 ffindnumberto { to < start next val > }

Like ffindnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.2.24 fskipnumber { < next start val > }

Optional arguments next, start and val specify names of the expression evaluator’s variables to which the position of the first character after the number, the position of the found number, and the value of the number are assigned, respectively. If the search is not successful then integer numbers less than 1 are assigned to next and start.

1.4.2.25 fskipnumberto { to < next start val > }

Like fskipnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.3 Reading the Data

1.4.3.1 freadnumber { varname <start next> }

Reads a number from the file infile and assigns its value to the expression evaluator’s variable named varname. Reading starts at the current position in the file. A number must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and a number). If the operation is successful, the current position in the file is set to the position of the first character after the read data.

An optional argument start specifies a name of the expression evaluator’s variable to which the current position in the file before the operation is assigned, and an optional argument next specifies a name of the expression evaluator’s variable to which the position of the first character after the read data is assigned. In the case that no data is read, the position before the operation is also assigned to the variable named next. These values are assigned to the expression evaluator’s variables named start and next regardless of the success of the operation, therefore the success can not be examined through the values of these variables, but only through registered errors.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the number can not be read, an appropriate error code is recorded.

1.4.3.2 freadnumberto { to varname <start next> }

Like freadnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.3.3 freadscalar { scalspec <start next> }

Reads a number from the file infile and assigns it to a programme’s scalar variable. scalspec is a specification of the variable to which the number is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A number must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and a number). If the operation is successful, the current position in the file is set to the position of the first character after the read data.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the scalar can not be read, an appropriate error code is recorded.

1.4.3.4 freadscalarto { to scalspec <start next> }

Like freadscalar, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.3.5 freadvector { vecspec <start next> }

Reads a vector from the file infile and assigns it to a programme’s vector variable. vecspec is a specification of the variable to which the read vector is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A vector must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and numbers of which the vector consists). The vector must be given as a sequence of numbers the first of which is vector’s dimension and the others are its components. All the components must be given and must follow in a successive order. If the operation is successful, the current position in the file is set to the position of the first character after the read data. If it is partially successful, the current position is set to the position of the first character after the last read number.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the vector can not be read, an appropriate error code is recorded. An error code is also recorded if only a part of the vector can be read.

1.4.3.6 freadvectorto { to vecspec <start next> }

Like freadvector, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.4.3.7 freadmatrix { matspec <start next> }

Reads a matrix from the file infile and assigns it to a programme’s matrix variable. matspec is a specification of the variable to which the read matrix is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A matrix must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and numbers of which the matrix consists). The matrix must be given as a sequence of numbers the first two of which are matrix’ dimensions and the others are its components. All the components must be given and must follow in a successive order (column indices changing quicker than row indices). If the operation is successful, the current position in the file is set to the position of the first character after the read data. If it is partially successful, the current position is set to the position of the first character after the last read number.

If the file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the matrix can not be read, an appropriate error code is recorded. An error code is also recorded if only a part of the matrix can be read.

1.4.3.8 freadmatrixto { to matspec <start next> }

Like freadmatrix, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5 File Interpreter Functions of the Interface which Operate on Arbitrary Files

1.5.1 Controlling the State of the Files

1.5.1.1 fprintfilepos { filespec }

Prints a report about the current position in the file specified by filespec to the shell's output file.

1.5.1.2 printfilepos { filespec }

Prints a report about the current position in the file specified by filespec to the standard output.

1.5.1.3 dprintfilepos { filespec }

Prints a report about the current position in the file specified by filespec to the standard output and the programme’s output file.

1.5.1.4 fprintfilepart { filespec pos1 <pos2> }

Prints a part of the file specified by filespec to the shell's output file. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is printed. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is printed. It prints the file part in the form of a report where it also prints which part of the file is printed.

An error is recorded if pos1 or pos2 are invalid. If filespec is not specified or the appropriate file variable is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.5.1.5 printfilepart { filespec pos1 <pos2> }

Does the same as fprintfilepart, except that it prints to standard output.

1.5.1.6 dprintfilepart { filespec pos1 <pos2> }

Does the same as fprintfilepart, except that it prints to the standard output and the programme’s output file.

1.5.1.7 fwritefilepart { filespec pos1 <pos2> }

Prints a part of the file specified by filespec to the shell's output file. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is printed. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is printed. Only the file part is printed without any explanation or newlines, so this function is useful if the user wants to use the contents of a file as a part of the output which he generates on his own way.

An error is recorded if pos1 or pos2 are invalid. If filespec is not specified or the file variable is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.5.1.8 writefilepart { filespec pos1 <pos2> }

Does the same as fwritefilepart, except that it prints to standard output.

1.5.1.9 dwritefilepart { filespec pos1 <pos2> }

Does the same as fwritefilepart, except that it prints to the standard output and the programme’s output file.

1.5.1.10 filesetpos { filespec pos }

Sets the current position in the file specified by filespec to the value of pos. pos should be a non-negative number not greater than the file size. If it is not an integer, it is rounded to the nearest integer. If it is zero, it is changed to the length of the file plus 1 before the operation is performed.

If it pos is greater than the length of the file, an error is recorded and the position is set to the end of the file (file length plus 1). If rounded pos is less than zero, an error is recorded and nothing else happens. If fiespec is not specified or the appropriate file variable is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.5.1.11 fileincreasepos { filespec inc }

Increases the current position in the file specified by filespec by inc. inc is rounded to the nearest integer. It can be negative (in this case the current position is decreased) or zero.

If filespec is not specified or the file variable is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.5.1.12 filemarkpos { filespec pos }

Marks the current position in the file specified by filespec. The position is assigned to the expression evaluator’s variable named pos. If the position can not be determined, an integer value less than 1 is assigned to the variable.

If filespec is not specified or the appropriate file variable is not defined, an error report is written to the standard output and to the programme’s output file. An error is not reported or recorded if the file is not connected to a physical file. In this case the marked position is less than one.

1.5.1.13 fileflush { filespec }

Empties the file buffer of the pre-defined file specified by filespec and writes the unsaved data on the disk.

1.5.2 Searching for the Data

1.5.2.1 filefindstring { filespec string <pos after> }

Searches for the string string in the file specified by filespec from the current position on. If the string is found, it sets the current position of this file to the first byte of the found string. pos and after are optional arguments which specify the names of expression evaluator's variables into which additional information is stored. The function assigns the position of the string to the variable named pos and the position of the first byte after the string to the variable named after.

1.5.2.2 filefindstringto { filespec to string <pos after> }

Like filefindstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.3 fileskipstring { filespec string <after pos> }

Searches for the string string in the file specified by filespec from the current position on. If the string is found, it sets the current position of this file to the first byte after the found string. Optional argument after specifies the name of the expression evaluator's variable to which the function assigns this position, and pos specifies the variable to which this function assigns the position of the found string (i.e. the first byte if this string if the file).

1.5.2.4 fileskipstringto { filespec to string <after pos> }

Like fileskipstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.5 filemultfindstring { filespec {string1 string2 string3 string4 ...} <which pos after> }

Searches for the first occurrence of any of the strings string1, string2, string3, etc. in the file specified by filespec from the current position on. If it finds any of these strings, it sets the current position to the position of the found string. Strings must be in curly brackets.

If argument which is given, the function assigns the ordinary number of the found string to the expression evaluator variable named which. If argument pos is given, the function assign the position of the found string to the expression evaluator's variable named pos. If after is also given, the function assign the position of the first byte after the found string to the variable with such name.

1.5.2.6 filemultfindstringto { filespec to {string1 string2 string3 string4 ...} <which pos after> }

Like filemultfindstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.7 filemultskipstring { filespec {string1 string2 string3 string4 ...} <which after pos> }

If argument which is given, the function assigns the ordinary number of the found string to the expression evaluator variable named which. If argument after is given, the function assign the position of the first byte of the found string to the expression evaluator's variable named after, and if pos is also specified, the function assign the position of the found string to the variable with such name.

1.5.2.8 filemultskipstringto { filespec to {string1 string2 string3 string4 ...} <which after pos> }

Like filemultskipstring, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.9 filefindcharacter {filespec charstring <pos> }

Searches in the file specified by filespec from the current position for the first occurrence of a character included in the string charstring. If the search is successful then it sets the current position in the file to the position of the found character.

1.5.2.10 filefindcharacterto { filespec to charstring <pos> }

Like filefindcharacter, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.11 fileskipcharacters { filespec charstring <pos> }

Searches in the file specified by filespec from the current position for the first occurrence of a character not included in the string charstring. If the search is successful then it sets the current position in the file to the position of the found character.

1.5.2.12 fileskipcharactersto { filespec to charstring <pos> }

Like fileskipcharacters, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.13 filefindblank { filespec <pos> }

Searches in the file specified by filespec from the current position for the first occurrence of a blank character, i.e. space, tab, newline, carriage return or null character. If the search is successful then it sets the current position in the file to the position of the found character.

1.5.2.14 filefindblankto { filespec to <pos> }

Like filefindblank, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.15 fileskipblanks { filespec file <pos> }

Searches in the file specified by filespec from the current position for the first occurrence of a non-blank character (blank characters are the space, tab, newline, carriage return and null character). If the search is successful then it sets the current position in the file to the position of the found character.

1.5.2.16 fileskipblanksto { filespec to <pos> }

Like fileskipblanks, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.17 filenextline { filespec <pos> }

Sets the current position in the file specified by filespec to the beginning of the next line from the current position in this file. If such position is found, it sets the current position in this file to it.

If filespec is not given or the appropriate file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the next line can not be located (e.g. when the current position is in the last line of the file), an appropriate error code is recorded.

1.5.2.18 filefindbrac { filespec bracstr <pos1 pos2> }

Searches in the file specified by filespec from the current position for the first occurrence of a closed bracket specified by bracstr. The first character of bracstr must be the character used for the opening bracket and the second character of the string must be the character used for the closing bracket. These characters may not be the same. Sequences which represent special characters can be used in this string. If the search is successful then the function sets the current position in the file to the position of the first character inside the bracket if the bracket contain any characters, otherwise it sets the current position to the position of the first character after the bracket.

If filespec is not given or the appropriate file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if a bracket is not found, an appropriate error code is recorded. An error code is also recorded if a bracket is found but does not contain any characters, i.e. the closing bracket immediately follow the opening bracket.

1.5.2.19 filefindbracto { filespec to bracstr <pos1 pos2> }

Like filefindbrac, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.20 fileskipbrac { filespec bracstr <pos1 pos2> }

Searches in the file specified by filespec from the current position for the first occurrence of a closed bracket specified by bracstr. The first character of bracstr must be the character used for the opening bracket and the second character of the string must be the character used for the closing bracket. These characters may not be the same. Sequences which represent special characters can be used in this string. If the search is successful then the function sets the current position in the to the position of the first character after the bracket.

1.5.2.21 fileskipbracto { filespec to bracstr <pos1 pos2> }

Like fileskipbrac, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.22 filefindnumber { filespec < start next val > }

Searches in the file specified by filespec from the current position for the first occurrence of a string which can represent a number. The number can be written in any standard format in which numbers are written in text files. If a number is found, the current position in the file is set to the position of the first character of the string which represent the number.

1.5.2.23 filefindnumberto { filespec to < start next val > }

Like filefindnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.2.24 fileskipnumber { filespec < next start val > }

1.5.2.25 fileskipnumberto { filespec to < next start val > }

Like fileskipnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.3 Reading the Data

1.5.3.1 filereadnumber { filespec varname <start next> }

Reads a number from the file specified by filespec and assigns its value to the expression evaluator’s variable named varname. Reading starts at the current position in the file. A number must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and a number). If the operation is successful, the current position in the file is set to the position of the first character after the read data.

1.5.3.2 filereadnumberto { filespec to varname <start next> }

Like filereadnumber, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.3.3 filereadscalar { filespec scalspec <start next> }

Reads a number from the file specified by filespec and assigns it to a programme’s scalar variable. scalspec is a specification of the variable to which the number is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A number must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and a number). If the operation is successful, the current position in the file is set to the position of the first character after the read data.

1.5.3.4 filereadscalarto { filespec to scalspec <start next> }

Like filereadscalar, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.3.5 filereadvector { filespec vecspec <start next> }

Reads a vector from the file specified by filespec and assigns it to a programme’s vector variable. vecspec is a specification of the variable to which the read vector is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A vector must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and numbers of which the vector consists). The vector must be given as a sequence of numbers the first of which is vector’s dimension and the others are its components. All the components must be given and must follow in a successive order. If the operation is successful, the current position in the file is set to the position of the first character after the read data. If it is partially successful, the current position is set to the position of the first character after the last read number.

If filespec is not given or the appropriate file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the vector can not be read, an appropriate error code is recorded. An error code is also recorded if only a part of the vector can be read.

1.5.3.6 filereadvectorto { filespec to vecspec <start next> }

Like filereadvector, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.3.7 filereadmatrix { filespec matspec <start next> }

Reads a matrix from the file specified by filespec and assigns it to a programme’s matrix variable. matspec is a specification of the variable to which the read matrix is assigned. It must be given in a standard form consisting of the variable name and optionally the index table in square brackets. Reading starts at the current position in the file. A matrix must reside at that position, otherwise the operation fails (blank characters are allowed between the current position and numbers of which the matrix consists). The matrix must be given as a sequence of numbers the first two of which are matrix’ dimensions and the others are its components. All the components must be given and must follow in a successive order (column indexes changing quicker than row indexes). If the operation is successful, the current position in the file is set to the position of the first character after the read data. If it is partially successful, the current position is set to the position of the first character after the last read number.

If filespec is not given or the appropriate file is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file or if the matrix can not be read, an appropriate error code is recorded. An error code is also recorded if only a part of the matrix can be read.

1.5.3.8 filereadmatrixto { filespec to matspec <start next> }

Like filereadmatrix, only that the operation is performed on a limited region of the file. Argument to specifies the upper limit of the action range.

1.5.4 Writing to Files and Copying File Parts

1.5.4.1 filewrite { filespec writespec }

Writes specified data in a specified format to the file specified by filespec. filespec is the specification of a file which consists of the file variable name and indexes of the file in the element table of this variable. writespec specifies what to write and in which form. The syntax of writespec is the same as at the functions fwrite and write. Writing begins at the current position of the file given by filespec. After the operation the current position is set to the first character after the written text.

An error report is written to the standard output and the programme’s output file if filespec is not specified and if the specified file variable does not exist or if the corresponding file is not open.

1.5.4.2 copyfpart { targetspec pos1 <pos2> }

Copies a part of the file infile to the file specified by targetspec. targetspec is the specification of a file which consists of the file variable name and indexes of the file in the element table of this variable. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is copied. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is copied.

The current position of the file infile remains unchanged while the current position of the file specified by targetspec is set to the first byte after the last copied byte.

An error is recorded if pos1 or pos2 are invalid. If the file infile is not defined, an error report is written to the standard output and to the programme’s output file. If it is not connected to a physical file, an appropriate error code is recorded.

1.5.4.3 copyfilepart { sourcespec targetspec pos1 <pos2> }

Copies a part of the file specified by sourcespec to the file specified by targetspec. sourcespec and targetspec are the specifications of files and consist of a file variable name and indexes of the file in the element table of the variable. If pos2 is specified, the part of the file from position pos1 to (including) pos2 is copied. If only pos1 is specified, pos1 bytes from the current position on (including the current position) of the file is copied.

The current position of the file specified by sourcespec remains unchanged while the current position of the file specified by targetspec is set to the first byte after the last copied byte.

An error is recorded if pos1 or pos2 are invalid. If any of the files specified by sourcespec or targerspec is not defined, an error report is written to the standard output and to the programme’s output file. If any of these files is not connected to a physical file, an appropriate error code is recorded.

1.6 Expression Evaluator’s Functions of the Interface