Source code in the cowgol programming language

include "cowgol.coh";
include "strings.coh";
include "malloc.coh";
include "argv.coh";
include "file.coh";

record Rule is
    pattern: [uint8];
    replacement: [uint8];
    next: [Rule];
    terminates: uint8;
end record;

sub AllocRule(): (rule: [Rule]) is       
    rule := Alloc(@bytesof Rule) as [Rule];
    MemZero(rule as [uint8], @bytesof Rule);
end sub;

sub ParseRule(text: [uint8]): (rule: [Rule]) is
    sub ParseError() is
        print("Failed to parse rule: ");
        print(text);
        print_nl();
        ExitWithError();
    end sub;
   
    var cur := text; 
    sub SkipWs() is 
        while [cur] != 0 and [cur] <= ' ' loop cur := @next cur; end loop; 
    end sub;
    
    sub AllocAndCopy(src: [uint8], length: intptr): (copy: [uint8]) is
        copy := Alloc(length + 1);
        MemCopy(src, length, copy);
        [copy + length] := 0;
    end sub;
          
    SkipWs();
    if [cur] == '#' or [cur] == 0 then # comment or empty line
        rule := 0 as [Rule];
        return;
    end if;
    var patternStart := cur;

    # find the " ->"
    while [cur] != 0 
    and ([cur] > ' ' or [cur+1] != '-' or [cur+2] != '>') loop
        cur := @next cur;
    end loop;
    if [cur] == 0 then ParseError(); end if;

    # find last char of pattern
    var patternEnd := cur;
    while patternStart < patternEnd and [patternEnd] <= ' ' loop
        patternEnd := @prev patternEnd;
    end loop;

    cur := cur + 3; # whitespace + '->'
    SkipWs();
    var replacementStart := cur;

    # find last char of replacement
    while [cur] != 0 loop cur := @next cur; end loop;
    while replacementStart < cur and [cur] <= ' ' loop
        cur := @prev cur;
    end loop;

    # make rule object
    rule := AllocRule();
    rule.pattern := AllocAndCopy(patternStart, patternEnd-patternStart+1);
    if [replacementStart] == '.' then
        rule.terminates := 1;
        replacementStart := @next replacementStart;
    end if;
    rule.replacement := AllocAndCopy(replacementStart, cur-replacementStart+1);
end sub;

sub FindMatch(needle: [uint8], haystack: [uint8]): (match: [uint8]) is
    match := 0 as [uint8];
    while [haystack] != 0 loop
        var n := needle;
        var h := haystack; 
        while [n] != 0 and [h] != 0 and [n] == [h] loop
            n := @next n;
            h := @next h;
        end loop;
        if [n] == 0 then
            match := haystack;
            return;
        end if;
        haystack := @next haystack;
    end loop;
end sub;

const NO_MATCH := 0;
const HALT := 1;
const CONTINUE := 2;
sub ApplyRule(rule: [Rule], in: [uint8], out: [uint8]): (result: uint8) is
    var match := FindMatch(rule.pattern, in);
    if match == 0 as [uint8] then
        result := NO_MATCH;
    else
        var len := StrLen(rule.replacement);
        var patlen := StrLen(rule.pattern);
        var rest := match + patlen;
        MemCopy(in, match-in, out);
        MemCopy(rule.replacement, len, out+(match-in));
        CopyString(rest, out+(match-in)+len);
        if rule.terminates != 0 then
            result := HALT;
        else
            result := CONTINUE;
        end if;
    end if;
end sub;

sub ApplyRules(rules: [Rule], buffer: [uint8]): (r: [uint8]) is
    var outbuf: uint8[256];
    var rule := rules;
    r := buffer;

    while rule != 0 as [Rule] loop
        case ApplyRule(rule, buffer, &outbuf[0]) is
            when NO_MATCH: 
                rule := rule.next;
            when HALT:
                CopyString(&outbuf[0], buffer);
                return;
            when CONTINUE:
                CopyString(&outbuf[0], buffer);
                rule := rules;
        end case;
    end loop;
end sub; 

sub ReadFile(filename: [uint8]): (rules: [Rule]) is
    var linebuf: uint8[256];
    var fcb: FCB;
    var bufptr := &linebuf[0];

    rules := 0 as [Rule];
    var prevRule := 0 as [Rule];

    if FCBOpenIn(&fcb, filename) != 0 then
        print("Cannot open file: ");
        print(filename);
        print_nl();
        ExitWithError();
    end if;
    
    var length := FCBExt(&fcb);
    var ch: uint8 := 1;
    while length != 0 and ch != 0 loop
        ch := FCBGetChar(&fcb);
        length := length - 1;
        [bufptr] := ch;
        bufptr := @next bufptr;

        if ch == '\n' then
            [bufptr] := 0;
            bufptr := &linebuf[0];
            var rule := ParseRule(&linebuf[0]);
            if rule != 0 as [Rule] then
                if rules == 0 as [Rule] then rules := rule; end if;
                if prevRule != 0 as [Rule] then prevRule.next := rule; end if;
                prevRule := rule;
            end if;
        end if;
    end loop;
    
    var dummy := FCBClose(&fcb);
end sub;

ArgvInit();
var fname := ArgvNext();
if fname == 0 as [uint8] then
    print("usage: markov [pattern file] [pattern]\n");
    ExitWithError();
end if;

var patbuf: uint8[256];
var patptr := &patbuf[0];
loop
    var patpart := ArgvNext();
    if patpart == 0 as [uint8] then
        if patptr != &patbuf[0] then patptr := @prev patptr; end if;
        [patptr] := 0;
        break;
    end if;
    var partlen := StrLen(patpart);
    MemCopy(patpart, partlen, patptr);
    patptr := patptr + partlen + 1;
    [@prev patptr] := ' ';
end loop;

print(ApplyRules(ReadFile(fname), &patbuf[0]));
print_nl();