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Annotation of 43BSD/contrib/kermit/ckwart.doc, revision 1.1

1.1     ! root        1: WART
        !             2: 
        !             3: Wart is a program that implements a small subset of the Unix 'lex' lexical
        !             4: analyzer generator.  Unlike lex, wart may be distributed without requirement
        !             5: for a Unix license.  Wart was written by Jeff Damens at the Columbia University
        !             6: Center of Computing Activities to facilitate development of Unix Kermit.
        !             7: 
        !             8: Wart is intended for production of state table switchers.  It allows a set of
        !             9: states to be defined, along with a function for getting input, and a table of
        !            10: state transitions.  A C program is generated which performs actions and
        !            11: switches states based on the current state and the input.
        !            12: 
        !            13: The following short program demonstrates some of the capabilities and
        !            14: limitations of Wart.  The program accepts from the command line a binary
        !            15: number, preceded by an optional minus sign, and optionally containing a
        !            16: fractional part.  It prints the decimal equivalent.
        !            17: 
        !            18: #include <stdio.h>
        !            19: 
        !            20: int state, s = 1, m = 0, d;
        !            21: float f;
        !            22: char *b;
        !            23: 
        !            24: %states sign mantissa fraction             /* Declare wart states */
        !            25: 
        !            26: %%                                         /* Begin state table */
        !            27: <sign>-      { s = -1; BEGIN mantissa; }    /* Look for sign */
        !            28: <sign>0      { m = 0;  BEGIN mantissa; }    /* Got digit, start mantissa */
        !            29: <sign>1      { m = 1;  BEGIN mantissa; }
        !            30: <sign>.      { fatal("bad input"); }       /* Detect bad format */
        !            31: <mantissa>0  { m *= 2; }                   /* Accumulate mantissa */
        !            32: <mantissa>1  { m = 2 * m + 1; }
        !            33: <mantissa>$  { printf("%d\n", s * m); return; }
        !            34: <mantissa>.  { f = 0.0; d = 1; BEGIN fraction; }    /* Start fraction */
        !            35: <fraction>0  { d *= 2; }                           /* Accumulate fraction */
        !            36: <fraction>1  { d *= 2; f += 1.0 / d; }
        !            37: <fraction>$  { printf("%f\n", s * (m + f) ); return; }
        !            38: <fraction>.  { fatal("bad input"); }
        !            39: %%
        !            40: 
        !            41: input() {                                  /* Define input() function */
        !            42:     int x;
        !            43:     return(((x = *b++) == '\0') ? '$' : x );
        !            44: }
        !            45: 
        !            46: fatal(s) char *s; {                        /* Error exit */
        !            47:     fprintf(stderr,"fatal - %s\n",s);
        !            48:     exit(1);
        !            49: }
        !            50: 
        !            51: main(argc,argv) int argc; char **argv; {    /* Main program */
        !            52:     if (argc < 1) exit(1);
        !            53:     b = *++argv;
        !            54:     state = sign;                          /* Initialize state */
        !            55:     wart();                                /* Invoke state switcher */
        !            56:     exit(0);                               /* Done */
        !            57: }
        !            58: 
        !            59: The wart program accepts as input a C program containing lines that start
        !            60: with "%" or sections delimited by "%%".  The directive "%states" declares
        !            61: the program's states.  The section enclosed by "%%" markers is the state
        !            62: table, with entries of the form
        !            63: 
        !            64:   <state>X { action }
        !            65: 
        !            66: which is read as "if in state <state> with input X perform { action }"
        !            67: 
        !            68: The optional <state> field tells the current state or states the program must
        !            69: be in to perform the indicated action.  If no state is specified, then it
        !            70: means the action will be performed regardless of the current state.  If more
        !            71: than one state is specifed, then the action will be performed in any of the
        !            72: listed states.  Multiple states are separated by commas.
        !            73: 
        !            74: The required input field consists of a single literal character.  When in
        !            75: the indicated state, if the input is the specified character, then the
        !            76: associated action will be performed.  The character '.' matches any input
        !            77: character.  No pattern matching or range notation is provided.  The input
        !            78: character is obtained from the input() function, which you must define.  It
        !            79: should be alphanumeric, or else one of the characters ".% -$@" (quotes not
        !            80: included).  Note that the program above recognize the binary point '.'
        !            81: through a ruse.
        !            82: 
        !            83: The action is a series of zero or more C language statements, enclosed in
        !            84: curly braces.
        !            85: 
        !            86: The BEGIN macro is defined simply to be "state = ", as in lex.
        !            87: 
        !            88: The wart() function is generated by the wart program based on the state
        !            89: declarations and the state transition table.  It loops through calls to
        !            90: input(), using the result to index into a big case statement it has created
        !            91: from the state table.
        !            92: 
        !            93: Wart is invoked as follows:
        !            94: 
        !            95:        wart          (Input from stdin, output to stdout)
        !            96: 
        !            97:        wart fn1      (Input from fn1, output to stdout)
        !            98: 
        !            99:        wart fn1 fn2  (Input from fn1, output to fn2.  Example:  wart a.w a.c)
        !           100: 
        !           101: Wart programs have the conventional filetype '.w'.

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