Added note about regexes
Getty Ritter
9 years ago
| 188 | 188 | but in the event that such structures arise, it would be better to switch from |
| 189 | 189 | NDBL to a proper data storage format. |
| 190 | 190 | |
| 191 | A Regular Language? | |
| 192 | ------------------- | |
| 193 | ||
| 194 | I asserted above that NDBL is a regular language. This is true in the sense | |
| 195 | that valid NDBL documents can be _recognized_ by a regular language. However, | |
| 196 | they cannot be _parsed_ by the kind of regular expressions that you have in | |
| 197 | most programming environments: this is because there is no well-founded way | |
| 198 | of matching a group underneath a Kleene star. We can construct a regular | |
| 199 | expression that matches a group: | |
| 200 | ||
| 201 | ~~~~ | |
| 202 | ([^# \t\r\n=][^ \t\r\n=]*)=("[^"|\\\\|\\"]*"|[^ \t\r\n=]*) | |
| 203 | ~~~~ | |
| 204 | ||
| 205 | We could also write a regular expression that maches entire NDBL documents, | |
| 206 | using here `{group}` as shorthand for the regex above: | |
| 207 | ||
| 208 | ~~~~ | |
| 209 | ({group}((#[^\r\n]*[\r\n]*[ \t]*|[\r\n]*[ \t])*{group})*[\r\n*])* | |
| 210 | ~~~~ | |
| 211 | ||
| 212 | But without | |
| 213 | [structural regular expressions](http://9p.io/sources/contrib/steve/other-docs/struct-regex.pdf) | |
| 214 | we cannot use this regex to actually pick apart the structure described | |
| 215 | by an NDBL document. | |
| 216 | ||
| 191 | 217 | Haskell API |
| 192 | 218 | ----------- |
| 193 | 219 |