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579 lines
18 KiB
Markdown
579 lines
18 KiB
Markdown
# V RegEx (Regular expression) 0.9g
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[TOC]
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## introduction
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Write here the introduction... not today!! -_-
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## Basic assumption
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In this release, during the writing of the code some assumptions are made and are valid for all the features.
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1. The matching stops at the end of the string not at the newline chars.
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2. The basic elements of this regex engine are the tokens, in a query string a simple char is a token. The token is the atomic unit of this regex engine.
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## Match positional limiter
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The module supports the following features:
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- `$` `^` delimiter
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`^` (Caret.) Matches at the start of the string
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`$` Matches at the end of the string
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## Tokens
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The tokens are the atomic units used by this regex engine and can be ones of the following:
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### Simple char
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this token is a simple single character like `a`.
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### Char class (cc)
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The cc matches all the chars specified inside, it is delimited by square brackets `[ ]`
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the sequence of chars in the class is evaluated with an OR operation.
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For example, the following cc `[abc]` matches any char that is `a` or `b` or `c` but doesn't match `C` or `z`.
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Inside a cc is possible to specify a "range" of chars, for example `[ad-f]` is equivalent to write `[adef]`.
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A cc can have different ranges at the same time like `[a-zA-z0-9]` that matches all the lowercase,uppercase and numeric chars.
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It is possible negate the cc using the caret char at the start of the cc like: `[^abc]` that matches every char that is not `a` or `b` or `c`.
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A cc can contain meta-chars like: `[a-z\d]` that matches all the lowercase latin chars `a-z` and all the digits `\d`.
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It is possible to mix all the properties of the char class together.
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**Note:** In order to match the `-` (minus) char, it must be located at the first position in the cc, for example `[-_\d\a]` will match `-` minus, `_`underscore, `\d` numeric chars, `\a` lower case chars.
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### Meta-chars
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A meta-char is specified by a backslash before a char like `\w` in this case the meta-char is `w`.
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A meta-char can match different type of chars.
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* `\w` matches an alphanumeric char `[a-zA-Z0-9_]`
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* `\W` matches a non alphanumeric char
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* `\d` matches a digit `[0-9]`
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* `\D` matches a non digit
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* `\s`matches a space char, one of `[' ','\t','\n','\r','\v','\f']`
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* `\S` matches a non space char
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* `\a` matches only a lowercase char `[a-z]`
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* `\A` matches only an uppercase char `[A-Z]`
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### Quantifier
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Each token can have a quantifier that specify how many times the char can or must be matched.
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#### **Short quantifier**
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- `?` matches 0 or 1 time, `a?b` matches both `ab` or `b`
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- `+` matches at minimum 1 time, `a+` matches both `aaa` or `a`
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- `*` matches 0 or more time, `a*b` matches both `aaab` or `ab` or `b`
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#### **Long quantifier**
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- `{x}` matches exactly x time, `a{2}` matches `aa` but doesn't match `aaa` or `a`
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- `{min,}` matches at minimum min time, `a{2,}` matches `aaa` or `aa` but doesn't match `a`
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- `{,max}` matches at least 0 time and maximum max time, `a{,2}` matches `a` and `aa` but doesn't match `aaa`
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- `{min,max}` matches from min times to max times, `a{2,3}` matches `aa` and `aaa` but doesn't match `a` or `aaaa`
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a long quantifier may have a `greedy off` flag that is the `?` char after the brackets, `{2,4}?` means to match the minimum number possible tokens in this case 2.
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### dot char
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the dot is a particular meta char that matches "any char", is more simple explain it with an example:
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suppose to have `abccc ddeef` as source string to parse with regex, the following table show the query strings and the result of parsing source string.
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| query string | result |
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| ------------ | ------ |
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| `.*c` | `abc` |
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| `.*dd` | `abcc dd` |
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| `ab.*e` | `abccc dde` |
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| `ab.{3} .*e` | `abccc dde` |
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the dot char matches any char until the next token match is satisfied.
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### OR token
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the token `|` is a logic OR operation between two consecutive tokens, `a|b` matches a char that is `a` or `b`.
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The OR token can work in a "chained way": `a|(b)|cd ` test first `a` if the char is not `a` then test the group `(b)` and if the group doesn't match test the token `c`.
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**note: The OR work at token level! It doesn't work at concatenation level!**
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A query string like `abc|bde` is not equal to `(abc)|(bde)`!! The OR work only on `c|b` not at char concatenation level.
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### Groups
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Groups are a method to create complex patterns with repetition of blocks of tokens.
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The groups are delimited by round brackets `( )`, groups can be nested and can have a quantifier as all the tokens.
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`c(pa)+z` match `cpapaz` or `cpaz` or `cpapapaz` .
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`(c(pa)+z ?)+` matches `cpaz cpapaz cpapapaz` or `cpapaz`
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let analyze this last case, first we have the group `#0` that are the most outer round brackets `(...)+`, this group has a quantifier that say to match its content at least one time `+`.
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After we have a simple char token `c` and a second group that is the number `#1` :`(pa)+`, this group try to match the sequence `pa` at least one time as specified by the `+` quantifier.
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After, we have another simple token `z` and another simple token ` ?` that is the space char (ascii code 32) followed by the `?` quantifier that say to capture the space char 0 or 1 time.
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This explain because the `(c(pa)+z ?)+` query string can match `cpaz cpapaz cpapapaz` .
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In this implementation the groups are "capture groups", it means that the last temporal result for each group can be retrieved from the `RE` struct.
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The "capture groups" are store as couple of index in the field `groups` that is an `[]int` inside the `RE` struct.
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**example:**
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```v
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text := "cpaz cpapaz cpapapaz"
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query:= r"(c(pa)+z ?)+"
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mut re := regex.regex_opt(query) or { panic(err) }
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println(re.get_query())
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// #0(c#1(pa)+z ?)+ // #0 and #1 are the ids of the groups, are shown if re.debug is 1 or 2
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start, end := re.match_string(text)
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// [start=0, end=20] match => [cpaz cpapaz cpapapaz]
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mut gi := 0
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for gi < re.groups.len {
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if re.groups[gi] >= 0 {
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println("${gi/2} :[${text[re.groups[gi]..re.groups[gi+1]]}]")
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}
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gi += 2
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}
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// groups captured
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// 0 :[cpapapaz]
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// 1 :[pa]
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```
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**note:** *to show the `group id number` in the result of the `get_query()` the flag `debug` of the RE object must be `1` or `2`*
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### Groups Continuous saving
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In particular situations it is useful have a continuous save of the groups, this is possible initializing the saving array field in `RE` struct: `group_csave`.
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This feature allow to collect data in a continuous way.
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In the example we pass a text followed by a integer list that we want collect.
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To achieve this task we can use the continuous saving of the group that save each captured group in a array that we set with: `re.group_csave = [-1].repeat(3*20+1)`.
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The array will be filled with the following logic:
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`re.group_csave[0]` number of total saved records
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`re.group_csave[1+n*3]` id of the saved group
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`re.group_csave[1+n*3]` start index in the source string of the saved group
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`re.group_csave[1+n*3]` end index in the source string of the saved group
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The regex save until finish or found that the array have no space. If the space ends no error is raised, further records will not be saved.
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```v
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fn example2() {
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test_regex()
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text := "tst: 01,23,45 ,56, 78"
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query:= r".*:(\s*\d+[\s,]*)+"
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mut re := new() or { panic(err) }
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//re.debug = 2
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re.group_csave = [-1].repeat(3*20+1) // we expect max 20 records
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re.compile_opt(query) or { println(err) return }
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q_str := re.get_query()
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println("Query: $q_str")
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start, end := re.match_string(text)
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if start < 0 {
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println("ERROR : ${re.get_parse_error_string(start)}, $start")
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} else {
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println("found in [$start, $end] => [${text[start..end]}]")
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}
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// groups capture
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mut gi := 0
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for gi < re.groups.len {
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if re.groups[gi] >= 0 {
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println("${gi/2} ${re.groups[gi]},${re.groups[gi+1]} :[${text[re.groups[gi]..re.groups[gi+1]]}]")
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}
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gi += 2
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}
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// continuous saving
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gi = 0
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println("num: ${re.group_csave[0]}")
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for gi < re.group_csave[0] {
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id := re.group_csave[1+gi*3]
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st := re.group_csave[1+gi*3+1]
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en := re.group_csave[1+gi*3+2]
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println("cg id: ${id} [${st}, ${en}] => [${text[st..en]}]")
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gi++
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}
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}
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```
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The output will be:
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```
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Query: .*:(\s*\d+[\s,]*)+
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found in [0, 21] => [tst: 01,23,45 ,56, 78]
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0 19,21 :[78]
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num: 5
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cg id: 0 [4, 8] => [ 01,]
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cg id: 0 [8, 11] => [23,]
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cg id: 0 [11, 15] => [45 ,]
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cg id: 0 [15, 19] => [56, ]
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cg id: 0 [19, 21] => [78]
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```
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### Named capturing groups
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This regex module support partially the question mark `?` PCRE syntax for groups.
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`(?:abcd)` **non capturing group**: the content of the group will not be saved
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`(?P<mygroup>abcdef)` **named group:** the group content is saved and labeled as `mygroup`
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The label of the groups is saved in the `group_map` of the `RE` struct, this is a map from `string` to `int` where the value is the index in `group_csave` list of index.
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Have a look at the example for the use of them.
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example:
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```v
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import regex
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fn main() {
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test_regex()
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text := "http://www.ciao.mondo/hello/pippo12_/pera.html"
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query:= r"(?P<format>https?)|(?:ftps?)://(?P<token>[\w_]+.)+"
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mut re := new()
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re.debug = 2
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// must provide an array of the right size if want the continuos saving of the groups
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re.group_csave = [-1].repeat(3*20+1)
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re.compile_opt(query) or { println(err) return }
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q_str := re.get_query()
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println("O.Query: $query")
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println("Query : $q_str")
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re.debug = 0
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start, end := re.match_string(text)
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if start < 0 {
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err_str := re.get_parse_error_string(start)
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println("ERROR : $err_str, $start")
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} else {
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text1 := text[start..end]
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println("found in [$start, $end] => [$text1]")
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}
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// groups
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mut gi := 0
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for gi < re.groups.len {
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if re.groups[gi] >= 0 {
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println("${gi/2} ${re.groups[gi]},${re.groups[gi+1]} :[${text[re.groups[gi]..re.groups[gi+1]]}]")
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}
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gi += 2
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}
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// continuous saving
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gi = 0
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println("num of group item saved: ${re.group_csave[0]}")
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for gi < re.group_csave[0] {
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id := re.group_csave[1+gi*3]
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st := re.group_csave[1+gi*3+1]
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en := re.group_csave[1+gi*3+2]
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println("cg id: ${id} [${st}, ${en}] => [${text[st..en]}]")
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gi++
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}
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println("raw array: ${re.group_csave[0..gi*3+2-1]}")
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// named capturing groups
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println("named capturing groups:")
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for g_name in re.group_map.keys() {
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s,e := re.get_group(g_name)
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if s >= 0 && e > s {
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println("'${g_name}':[$s, $e] => '${text[s..e]}'")
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} else {
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println("Group [${g_name}] doesn't exist.")
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}
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}
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}
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```
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Output:
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```
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O.Query: (?P<format>https?)|(?:ftps?)://(?P<token>[\w_]+.)+
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Query : #0(?P<format>https?)|{8,14}(?:ftps?)://#1(?P<token>[\w_]+.)+
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found in [0, 46] => [http://www.ciao.mondo/hello/pippo12_/pera.html]
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0 0,4 :[http]
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1 42,46 :[html]
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num of group item saved: 8
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cg id: 0 [0, 4] => [http]
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cg id: 1 [7, 11] => [www.]
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cg id: 1 [11, 16] => [ciao.]
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cg id: 1 [16, 22] => [mondo/]
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cg id: 1 [22, 28] => [hello/]
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cg id: 1 [28, 37] => [pippo12_/]
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cg id: 1 [37, 42] => [pera.]
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cg id: 1 [42, 46] => [html]
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raw array: [8, 0, 0, 4, 1, 7, 11, 1, 11, 16, 1, 16, 22, 1, 22, 28, 1, 28, 37, 1, 37, 42, 1, 42, 46]
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named capturing groups:
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'format':[0, 4] => 'http'
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'token':[42, 46] => 'html'
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```
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## Flags
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It is possible to set some flags in the regex parser that change the behavior of the parser itself.
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```v
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// example of flag settings
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mut re := regex.new()
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re.flag = regex.F_BIN
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```
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- `F_BIN`: parse a string as bytes, utf-8 management disabled.
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- `F_EFM`: exit on the first char matches in the query, used by the find function.
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- `F_MS`: matches only if the index of the start match is 0, same as `^` at the start of the query string.
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- `F_ME`: matches only if the end index of the match is the last char of the input string, same as `$` end of query string.
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- `F_NL`: stop the matching if found a new line char `\n` or `\r`
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## Functions
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### Initializer
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These functions are helper that create the `RE` struct, a `RE` struct can be created manually if you needed.
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#### **Simplified initializer**
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```v
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// regex create a regex object from the query string and compile it
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pub fn regex_opt(in_query string) ?RE
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```
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#### **Base initializer**
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```v
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// new_regex create a REgex of small size, usually sufficient for ordinary use
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pub fn new() RE
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// new_regex_by_size create a REgex of large size, mult specify the scale factor of the memory that will be allocated
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pub fn new_by_size(mult int) RE
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```
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After a base initializer is used, the regex expression must be compiled with:
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```v
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// compile compiles the REgex returning an error if the compilation fails
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pub fn (re mut RE) compile_opt(in_txt string) ?
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```
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### Operative Functions
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These are the operative functions
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```v
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// match_string try to match the input string, return start and end index if found else start is -1
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pub fn (re mut RE) match_string(in_txt string) (int,int)
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// find try to find the first match in the input string, return start and end index if found else start is -1
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pub fn (re mut RE) find(in_txt string) (int,int)
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// find_all find all the "non overlapping" occurrences of the matching pattern, return a list of start end indexes
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pub fn (re mut RE) find_all(in_txt string) []int
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// replace return a string where the matches are replaced with the replace string, only non overlapped matches are used
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pub fn (re mut RE) replace(in_txt string, repl string) string
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```
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## Debugging
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This module has few small utilities to help the writing of regex expressions.
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### **Syntax errors highlight**
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the following example code show how to visualize the syntax errors in the compilation phase:
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```v
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query:= r"ciao da ab[ab-]" // there is an error, a range not closed!!
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mut re := new()
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re.compile_opt(query) or { println(err) }
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// output!!
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//query: ciao da ab[ab-]
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//err : ----------^
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//ERROR: ERR_SYNTAX_ERROR
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```
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### **Compiled code**
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It is possible view the compiled code calling the function `get_query()` the result will be something like this:
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```
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========================================
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v RegEx compiler v 0.9c output:
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PC: 0 ist: 7fffffff [a] query_ch { 1, 1}
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PC: 1 ist: 7fffffff [b] query_ch { 1,MAX}
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PC: 2 ist: 88000000 PROG_END { 0, 0}
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========================================
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```
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`PC`:`int` is the program counter or step of execution, each single step is a token.
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`ist`:`hex` is the token instruction id.
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`[a]` is the char used by the token.
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`query_ch` is the type of token.
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`{m,n}` is the quantifier, the greedy off flag `?` will be showed if present in the token
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### **Log debug**
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The log debugger allow to print the status of the regex parser when the parser is running.
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It is possible to have two different level of debug: 1 is normal while 2 is verbose.
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here an example:
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*normal*
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list only the token instruction with their values
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```
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// re.flag = 1 // log level normal
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flags: 00000000
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# 2 s: ist_load PC: 0=>7fffffff i,ch,len:[ 0,'a',1] f.m:[ -1, -1] query_ch: [a]{1,1}:0 (#-1)
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# 5 s: ist_load PC: 1=>7fffffff i,ch,len:[ 1,'b',1] f.m:[ 0, 0] query_ch: [b]{2,3}:0? (#-1)
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# 7 s: ist_load PC: 1=>7fffffff i,ch,len:[ 2,'b',1] f.m:[ 0, 1] query_ch: [b]{2,3}:1? (#-1)
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# 10 PROG_END
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```
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|
*verbose*
|
|
|
|
list all the instructions and states of the parser
|
|
|
|
```
|
|
flags: 00000000
|
|
# 0 s: start PC: NA
|
|
# 1 s: ist_next PC: NA
|
|
# 2 s: ist_load PC: 0=>7fffffff i,ch,len:[ 0,'a',1] f.m:[ -1, -1] query_ch: [a]{1,1}:0 (#-1)
|
|
# 3 s: ist_quant_p PC: 0=>7fffffff i,ch,len:[ 1,'b',1] f.m:[ 0, 0] query_ch: [a]{1,1}:1 (#-1)
|
|
# 4 s: ist_next PC: NA
|
|
# 5 s: ist_load PC: 1=>7fffffff i,ch,len:[ 1,'b',1] f.m:[ 0, 0] query_ch: [b]{2,3}:0? (#-1)
|
|
# 6 s: ist_quant_p PC: 1=>7fffffff i,ch,len:[ 2,'b',1] f.m:[ 0, 1] query_ch: [b]{2,3}:1? (#-1)
|
|
# 7 s: ist_load PC: 1=>7fffffff i,ch,len:[ 2,'b',1] f.m:[ 0, 1] query_ch: [b]{2,3}:1? (#-1)
|
|
# 8 s: ist_quant_p PC: 1=>7fffffff i,ch,len:[ 3,'b',1] f.m:[ 0, 2] query_ch: [b]{2,3}:2? (#-1)
|
|
# 9 s: ist_next PC: NA
|
|
# 10 PROG_END
|
|
# 11 PROG_END
|
|
```
|
|
|
|
the columns have the following meaning:
|
|
|
|
`# 2` number of actual steps from the start of parsing
|
|
|
|
`s: ist_next` state of the present step
|
|
|
|
`PC: 1` program counter of the step
|
|
|
|
`=>7fffffff ` hex code of the instruction
|
|
|
|
`i,ch,len:[ 0,'a',1]` `i` index in the source string, `ch` the char parsed, `len` the length in byte of the char parsed
|
|
|
|
`f.m:[ 0, 1]` `f` index of the first match in the source string, `m` index that is actual matching
|
|
|
|
`query_ch: [b]` token in use and its char
|
|
|
|
`{2,3}:1?` quantifier `{min,max}`, `:1` is the actual counter of repetition, `?` is the greedy off flag if present
|
|
|
|
### **Custom Logger output**
|
|
|
|
The debug functions output uses the `stdout` as default, it is possible to provide an alternative output setting a custom output function:
|
|
|
|
```v
|
|
// custom print function, the input will be the regex debug string
|
|
fn custom_print(txt string) {
|
|
println("my log: $txt")
|
|
}
|
|
|
|
mut re := new()
|
|
re.log_func = custom_print // every debug output from now will call this function
|
|
|
|
```
|
|
|
|
## Example code
|
|
|
|
Here there is a simple code to perform some basically match of strings
|
|
|
|
```v
|
|
struct TestObj {
|
|
source string // source string to parse
|
|
query string // regex query string
|
|
s int // expected match start index
|
|
e int // expected match end index
|
|
}
|
|
const (
|
|
tests = [
|
|
TestObj{"this is a good.",r"this (\w+) a",0,9},
|
|
TestObj{"this,these,those. over",r"(th[eio]se?[,. ])+",0,17},
|
|
TestObj{"test1@post.pip.com, pera",r"[\w]+@([\w]+\.)+\w+",0,18},
|
|
TestObj{"cpapaz ole. pippo,",r".*c.+ole.*pi",0,14},
|
|
TestObj{"adce aabe",r"(a(ab)+)|(a(dc)+)e",0,4},
|
|
]
|
|
)
|
|
|
|
fn example() {
|
|
for c,tst in tests {
|
|
mut re := regex.new()
|
|
re.compile_opt(tst.query) or { println(err) continue }
|
|
|
|
// print the query parsed with the groups ids
|
|
re.debug = 1 // set debug on at minimum level
|
|
println("#${c:2d} query parsed: ${re.get_query()}")
|
|
re.debug = 0
|
|
|
|
// do the match
|
|
start, end := re.match_string(tst.source)
|
|
if start >= 0 && end > start {
|
|
println("#${c:2d} found in: [$start, $end] => [${tst.source[start..end]}]")
|
|
}
|
|
|
|
// print the groups
|
|
mut gi := 0
|
|
for gi < re.groups.len {
|
|
if re.groups[gi] >= 0 {
|
|
println("group ${gi/2:2d} :[${tst.source[re.groups[gi]..re.groups[gi+1]]}]")
|
|
}
|
|
gi += 2
|
|
}
|
|
println("")
|
|
}
|
|
}
|
|
|
|
fn main() {
|
|
example()
|
|
}
|
|
```
|
|
|
|
more example code is available in the test code for the `regex` module `vlib\regex\regex_test.v`.
|
|
|