421 lines
14 KiB
Markdown
421 lines
14 KiB
Markdown
# V RegEx (Regular expression) 0.9c
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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 match 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]` match 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 match 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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### 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` match an alphanumeric char `[a-zA-Z0-9]`
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* `\W` match a non alphanumeric char
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* `\d` match a digit `[0-9]`
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* `\D` match a non digit
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* `\s`match a space char, one of `[' ','\t','\n','\r','\v','\f']`
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* `\S` match a non space char
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* `\a` match only a lowercase char `[a-z]`
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* `\A` match 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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- `?` match 0 or 1 time, `a?b` match both `ab` or `b`
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- `+` match at minimum 1 time, `a+` match both `aaa` or `a`
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- `*` match 0 or more time, `a*b` match both `aaab` or `ab` or `b`
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#### **Long quantifier**
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- `{x}` match exactly x time, `a{2}` match `aa` but doesn't match `aaa` or `a`
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- `{min,}` match at minimum min time, `a{2,}` match `aaa` or `aa` but doesn't match `a`
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- `{,max}` match at least 0 time and maximum max time, `a{,2}` match `a` and `aa` but doesn't match `aaa`
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- `{min,max}` match from min times to max times, `a{2,3}` match `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 match "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 match 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` match 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 ?)+` match `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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re, _, _ := regex.regex(query)
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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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## 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_regex()
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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 match in the query, used by the find function.
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- `F_MS`: match 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`: match 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(in_query string) (RE,int,int)
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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_regex() 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_regex_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 return (return code, index) where index is the index of the error in the query string if return code is an error code
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pub fn (re mut RE) compile(in_txt string) (int,int)
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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_regex()
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// re_err ==> is the return value, if < 0 it is an error
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// re_pos ==> if re_err < 0, re_pos is the error index in the query string
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re_err, err_pos := re.compile(query)
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// print the error if one happen
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if re_err != COMPILE_OK {
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println("query: $query")
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lc := "-".repeat(err_pos)
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println("err : $lc^")
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err_str := re.get_parse_error_string(re_err) // get the error string
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println("ERROR: $err_str")
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}
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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*
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list all the instructions and states of the parser
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```
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flags: 00000000
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# 0 s: start PC: NA
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# 1 s: ist_next PC: NA
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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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# 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)
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# 4 s: ist_next PC: NA
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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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# 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)
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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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# 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)
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# 9 s: ist_next PC: NA
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# 10 PROG_END
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# 11 PROG_END
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```
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the columns have the following meaning:
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`# 2` number of actual steps from the start of parsing
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`s: ist_next` state of the present step
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`PC: 1` program counter of the step
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`=>7fffffff ` hex code of the instruction
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`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
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`f.m:[ 0, 1]` `f` index of the first match in the source string, `m` index that is actual matching
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`query_ch: [b]` token in use and its char
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`{2,3}:1?` quantifier `{min,max}`, `:1` is the actual counter of repetition, `?` is the greedy off flag if present
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### **Custom Logger output**
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The debug functions output uses the `stdout` as default, it is possible to provide an alternative output setting a custom output function:
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```v
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// custom print function, the input will be the regex debug string
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fn custom_print(txt string) {
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println("my log: $txt")
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}
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mut re := new_regex()
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re.log_func = custom_print // every debug output from now will call this function
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```
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## Example code
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Here there is a simple code to perform some basically match of strings
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```v
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struct TestObj {
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source string // source string to parse
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query string // regex query string
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s int // expected match start index
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e int // expected match end index
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}
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const (
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tests = [
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TestObj{"this is a good.",r"this (\w+) a",0,9},
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TestObj{"this,these,those. over",r"(th[eio]se?[,. ])+",0,17},
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TestObj{"test1@post.pip.com, pera",r"[\w]+@([\w]+\.)+\w+",0,18},
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TestObj{"cpapaz ole. pippo,",r".*c.+ole.*pi",0,14},
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TestObj{"adce aabe",r"(a(ab)+)|(a(dc)+)e",0,4},
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]
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)
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fn example() {
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for c,tst in tests {
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mut re := regex.new_regex()
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re_err, err_pos := re.compile(tst.query)
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if re_err == regex.COMPILE_OK {
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// print the query parsed with the groups ids
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re.debug = 1 // set debug on at minimum level
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println("#${c:2d} query parsed: ${re.get_query()}")
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re.debug = 0
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// do the match
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start, end := re.match_string(tst.source)
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if start >= 0 && end > start {
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println("#${c:2d} found in: [$start, $end] => [${tst.source[start..end]}]")
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}
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// print the 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("group ${gi/2:2d} :[${tst.source[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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println("")
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} else {
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// print the compile error
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println("query: $tst.query")
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lc := "-".repeat(err_pos-1)
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println("err : $lc^")
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err_str := re.get_parse_error_string(re_err)
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println("ERROR: $err_str")
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}
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}
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}
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fn main() {
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example()
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}
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```
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more example code is available in the test code for the `regex` module `vlib\regex\regex_test.v`.
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