Objective-c中的脚本阅读器

Question

I am trying to make a simple markup language, and I need my Cocoa app to be able to read it. I would prefer to have that code written in Objective-c, but I am happy to use any other language.

Here is my current problem. I am using this code:

for (int character = 1; character < ([script length] - 1); character ++) {
    NSLog(@"%@", [[script substringToIndex:character] substringFromIndex:([[script substringToIndex:character] length] - 2)]);

Unfortunately, if I pass the string [button] through it, it shows this in the debug console:

[
[b
[bu
[but
[butt
[__NSCFConstantString substringWithRange:]: Range or index out of bounds

I can sort out the error message, but I need to know how to read the script and recognize certain tags like [button] . Can anybody give me a link to something useful on this subject?

Answer 1

This all depends on how complex your scripting language is intended to be, and how efficient and robust it needs to be.

In general, if you don't need a rich syntax, you might be best using XML or JSON for your syntax, and just applying your own semantics to one of those.

Otherwise, parsing is a fairly large, complex field within programming, and you should study up a bit before you dive in (there are dozens of good references, on the web and in books). I've written 20 or so "simple" parsers over my decades of experience, and I can attest that it's never as easy as you expect.

Answer 2

Just to give you examples:

NSString *str = @"[Button]";
NSUInteger i, len = [str length];

for (i = 1; i <= len; ++i)
    NSLog(@"%@", [str substringToIndex:i]);

for (i = 0; i < len; ++i)
    NSLog(@"%c", [str characterAtIndex:i]);

Output:

[
[B
[Bu
[But
[Butt
[Butto
[Button
[Button]
[
B
u
t
t
o
n
]

And a more interesting case:

for (i = 0; i < len; ++i)
    NSLog([NSString stringWithFormat:@"%%%dc", i+1],
          [str characterAtIndex:i]);

Which produces:

[
 B
  u
   t
    t
     o
      n
       ]