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Simple ParseKit Grammar for HTML with Replacement Variables

For an iOS application, I want to parse an HTML file that may contain UNIX style variables for replacement. For example, HTML might look like this:

<html>
  <head></head>
  <body>
    <h1>${title}</h1>
    <p>${paragraph1}</p>
    <img src="${image}" />
  </body>
</html>

I am trying to create a simple ParseKit grammar that will provide me with two callbacks: one for pass-through HTML, and the other for variables that it detects. To do this, I created the following grammar:

@start        = Empty | content*;

content       = variable | passThrough;
passThrough   = /[^$]+/;
variable      = '$' '{' Word closeChar;

openChar      = '${';
closeChar     = '}';

I have at least two problems with this: for variableI initially declared it as openChar Word closeChar, but it did not work (I still don't know why). The second problem (and, more importantly) is that the parser stops when it finds it <img src"${image}" />(i.e. the variable inside the quoted string).

My questions:

  • How can I change the grammar so that it works properly?
  • ? , ?
+5
1

ParseKit . :

1) , . , .

, :

// Tokenizer Directives
@symbolState = '"' "'"; // effectively tells the tokenizer to turn off QuoteState. 
                      // Otherwise, variables enclosed in quotes would not be found (they'd be embedded in quoted strings). 
                      // now single- & double-quotes will be recognized as individual symbols, not start- & end-markers for quoted strings

@symbols = '${'; // declare '${' as a multi-char symbol

@reportsWhitespaceTokens = YES; // tell the tokenizer to preserve/report whitespace

// Grammar
@start = content*;
content = passthru | variable;
passthru = /[^$].*/;
variable = start name end;
start = '${';
end = '}';
name = Word;

:

- (void)parser:(PKParser *)p didMatchName:(PKAssembly *)a {
    NSLog(@"%s %@", __PRETTY_FUNCTION__, a);
    PKToken *tok = [a pop];

    NSString *name = tok.stringValue;
    // do something with name
}

- (void)parser:(PKParser *)p didMatchPassthru:(PKAssembly *)a {
    NSLog(@"%s %@", __PRETTY_FUNCTION__, a);
    PKToken *tok = [a pop];

    NSMutableString *s = a.target;
    if (!s) {
        s = [NSMutableString string];
    }

    [s appendString:tok.stringValue];

    a.target = s;
}

/ :

NSString *g = // fetch grammar
PKParser *p = [[PKParserFactory factory] parserFromGrammar:g assembler:self];
NSString *s = @"<img src=\"${image}\" />";
[p parse:s];
NSString *result = [p parse:s];
NSLog(@"result %@", result);

:

result: <img src="" />

2) , , Tokenizer . . Tokenizer:

PKTokenizer *t = [PKTokenizer tokenizerWithString:s];
[t setTokenizerState:t.symbolState from:'"' to:'"'];
[t setTokenizerState:t.symbolState from:'\'' to:'\''];
[t.symbolState add:@"${"];
t.whitespaceState.reportsWhitespaceTokens = YES;

NSMutableString *result = [NSMutableString string];

PKToken *eof = [PKToken EOFToken];
PKToken *tok = nil;
while (eof != (tok = [t nextToken])) {
    if ([@"${" isEqualToString:tok.stringValue]) {
        tok = [t nextToken];
        NSString *varName = tok.stringValue;

        // do something with variable
    } else if ([@"}" isEqualToString:tok.stringValue]) {
        // do nothing
    } else {
        [result appendString:tok.stringValue];
    }
}
+4

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