Dumb Interpretively Evaluated String Expression Language

This “Dumb Interpretively Executed String Expression Language” is the kernel of a macro language you can customise by adding C code and embedding it into your program.

It is short, written in portable C, and is readily integrated into any program. It is useful primarily to programs which need a very rudimentary macro expansion facility without the complexity of a full language such as Lisp or FORTH.

DIESEL copies its input directly to the output until a macro character, “$” or quoted string is encountered. Quoted strings may be used to suppress evaluation of sequences of characters which would otherwise be interpreted as macros. Quote marks may be included in quoted strings by two adjacent quote marks. For example:


Status retrieval, computation, and display are performed by DIESEL functions. The available functions are as follows. User-defined functions are not implemented; what you see is all you've got. Naturally, if you embed DIESEL in your application, you'll add functions that provide access to information and actions within your own program. DIESEL's arithmetic functions accept either floating point or integer arguments, and perform all calculations in floating point.

DIESEL String Functions

The sum of the numbers val1, val2,…valn is returned.
The result of subtracting the numbers val2 through valn from val1 is returned.
The result of multiplying the numbers val1,val2,…valn is returned.
The result of dividing the number val1 by val2,…valn is returned.
If the numbers val1 and val2 are equal 1 is returned, otherwise 0 is returned.
If the number val1 is less than val2 1 is returned, otherwise 0 is returned.
If the number val1 is greater than val2 1 is returned, otherwise 0 is returned.
If the numbers val1 and val2 are not equal 1 is returned, otherwise 0 is returned.
If the number val1 is less than or equal to val2 1 is returned, otherwise 0 is returned.
If the number val1 is greater than or equal to val2 1 is returned, otherwise 0 is returned.
The bitwise logical AND of the integers val1 through valn is returned.
If the strings val1 and val2 are identical 1 is returned, otherwise 0.
The string str is passed to the DIESEL evaluator and the result of evaluating it is returned.
The real number value is truncated to an integer by discarding any fractional part.
If expr is nonzero, dotrue is evaluated and returned. Otherwise, dofalse is evaluated and returned. Note that the branch not chosen by expr is not evaluated.
string is assumed to contain one or more values delimited by the macro argument separator character, comma. which selects one of these values to be extracted, with the first item numbered zero.
Evaluates and returns the argument selected by which. If which is 0, arg0 is returned, and so on. Note the difference between $(NTH) and $(INDEX); $(NTH) returns one of a series of arguments to the function while $(INDEX) extracts a value from a comma-delimited string passed as a single argument. Arguments not selected by which are not evaluated.
The bitwise logical OR of the integers val1 through valn is returned.
Returns the result of concatenating ncopies of string.
Returns the length of string in characters.
Returns the substring of string starting at character start and extending for length characters. Characters in the string are numbered from 1. If length is omitted, the entire remaining length of the string is returned.
The string is returned converted to upper case according to the rules of the current locale.
The bitwise logical XOR of the integers val1 through valn is returned.

Starting DIESEL

You invoke DIESEL within your program by calling:

    int status;
    char instring[whatever], outstring[MAXSTR + 1];

    status = diesel(instring, outstring);

The output from the evaluation will be stored in outstring when control is returned to your program. If no errors were detected during evaluation, status will be zero. Otherwise status gives the character position within instring at which the error was detected. If an error occurs, DIESEL will include an error diagnostic, documented below, in outstring.

DIESEL Mechanics

Generally, if you mess something up in a DIESEL expression it's pretty obvious what went wrong. DIESEL embeds an error indication in the output stream depending on the nature of the error:

Syntax error (usually a missing right parenthesis or runaway string).
Incorrect arguments to func.
Unknown function func.
Output string too long—evaluation truncated.

Variable Extensions

The base-line DIESEL includes no user-defined variables. This allows DIESEL to avoid allocating any local memory and renders it totally reentrant. If you compile DIESEL with the tag VARIABLES defined, the following additional functions are included which provide variable definition and access. Note that these functions call malloc() and strdup() and thus consume heap storage.

Returns the value stored in varname. If no variable with the name varname exists, a bad argument error is reported.
Stores the string value into varname. If no variable called varname exists, a new variable is created.

Unix Extensions

If you compile DIESEL with the tag UNIXTENSIONS defined, the following additional functions will be available:

Returns the variable varname from the environment. If no such variable is defined, returns the null string.
Returns the current time in Unix fashion, as the number of seconds elapsed since 00:00:00 GMT January 1, 1970.
Edit the Unix time time to format picture. If time is 0, the current date and time is edited (this is just shorthand for the equivalent “$(EDTIME,$(TIME),picture)”).

Assume the date is: Thursday, 2 September 1993 4:53:17

Format phrases:

        D               2
        DD              02
        DDD             Thu
        DDDD            Thursday
        M               9
        MO              09
        MON             Sep
        MONTH           September
        YY              93
        YYYY            1993
        H               4
        HH              04
        MM              53
        SS              17
        AM/PM           AM
        am/pm           am
        A/P             A
        a/p             a
If any of the “AM/PM” phrases appear in the picture, the “H” and “HH” phrases will edit the time according to the 12 hour civil clock (12:00–12:59—1:00–11:59) instead of the 24 hour clock (00:00–23:59).

Distribution Details

DIESEL is in the public domain; you can do anything you like with it.

DIESEL is supplied as a GZIPped TAR archive, diesel.tar.gz.

The following files will be present in the directory after the extraction is complete:

BCMAKE.BAT      Batch file to build with Borland C on MS-DOS.
DIESEL.C        Complete source code, including a built-in test
MAKEFILE        Make file for Unix.
MANIFEST        List of files in the distribution.
MSCMAKE.BAT     Batch file to build with Microsoft C 7.0.
REGRESS.DSL     Diesel regression test script.
REGRESS.MAS     Regression test master output file.
UTEST.DSL       Test for the Unix extensions to DIESEL.

All files are distributed in MS-DOS end of line convention (CR/LF). You may have to convert them to the native end of line convention of your system before compiling. DIESEL has been built and regression tested without errors on the following systems:

    Sun SPARCStation 2, SunOS 4.1.1
    MS-DOS, Borland C 2.0
    MS-DOS, Microsoft C 7.0

DIESEL Power Not Enough?

If DIESEL looks intriguing, but too small and simple for the application you have in mind, please check out ATLAST, my FORTH-based open application toolkit. ATLAST, although much larger and more complicated than DIESEL, is a full-fledged programming language which provides the speed of compiled code, multiple data types, user-defined functions and data types, and just about everything you'll need to make a closed application user programmable.

by John Walker