Documentation
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Overview ¶
Package syntax parses regular expressions into parse trees and compiles parse trees into programs. Most clients of regular expressions will use the facilities of package regexp (such as Compile and Match) instead of this package.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func IsWordChar ¶
IsWordChar reports whether r is consider a “word character” during the evaluation of the \b and \B zero-width assertions. These assertions are ASCII-only: the word characters are [A-Za-z0-9_].
Types ¶
type EmptyOp ¶
type EmptyOp uint8
An EmptyOp specifies a kind or mixture of zero-width assertions.
func EmptyOpContext ¶
EmptyOpContext returns the zero-width assertions satisfied at the position between the runes r1 and r2. Passing r1 == -1 indicates that the position is at the beginning of the text. Passing r2 == -1 indicates that the position is at the end of the text.
type Error ¶
An Error describes a failure to parse a regular expression and gives the offending expression.
type ErrorCode ¶
type ErrorCode string
An ErrorCode describes a failure to parse a regular expression.
const ( // Unexpected error ErrInternalError ErrorCode = "regexp/syntax: internal error" // Parse errors ErrInvalidCharClass ErrorCode = "invalid character class" ErrInvalidCharRange ErrorCode = "invalid character class range" ErrInvalidEscape ErrorCode = "invalid escape sequence" ErrInvalidNamedCapture ErrorCode = "invalid named capture" ErrInvalidPerlOp ErrorCode = "invalid or unsupported Perl syntax" ErrInvalidRepeatOp ErrorCode = "invalid nested repetition operator" ErrInvalidRepeatSize ErrorCode = "invalid repeat count" ErrInvalidUTF8 ErrorCode = "invalid UTF-8" ErrMissingBracket ErrorCode = "missing closing ]" ErrMissingParen ErrorCode = "missing closing )" ErrMissingRepeatArgument ErrorCode = "missing argument to repetition operator" ErrTrailingBackslash ErrorCode = "trailing backslash at end of expression" )
type Flags ¶
type Flags uint16
Flags control the behavior of the parser and record information about regexp context.
const ( FoldCase Flags = 1 << iota // case-insensitive match Literal // treat pattern as literal string ClassNL // allow character classes like [^a-z] and [[:space:]] to match newline DotNL // allow . to match newline OneLine // treat ^ and $ as only matching at beginning and end of text NonGreedy // make repetition operators default to non-greedy PerlX // allow Perl extensions UnicodeGroups // allow \p{Han}, \P{Han} for Unicode group and negation WasDollar // regexp OpEndText was $, not \z Simple // regexp contains no counted repetition MatchNL = ClassNL | DotNL Perl = ClassNL | OneLine | PerlX | UnicodeGroups // as close to Perl as possible POSIX Flags = 0 // POSIX syntax )
type Inst ¶
type Inst struct {
Op InstOp
Out uint32 // all but InstMatch, InstFail
Arg uint32 // InstAlt, InstAltMatch, InstCapture, InstEmptyWidth
Rune []rune
}
An Inst is a single instruction in a regular expression program.
func (*Inst) MatchEmptyWidth ¶
MatchEmptyWidth returns true if the instruction matches an empty string between the runes before and after. It should only be called when i.Op == InstEmptyWidth.
type Op ¶
type Op uint8
An Op is a single regular expression operator.
const ( OpNoMatch Op = 1 + iota // matches no strings OpEmptyMatch // matches empty string OpLiteral // matches Runes sequence OpCharClass // matches Runes interpreted as range pair list OpAnyCharNotNL // matches any character OpAnyChar // matches any character OpBeginLine // matches empty string at beginning of line OpEndLine // matches empty string at end of line OpBeginText // matches empty string at beginning of text OpEndText // matches empty string at end of text OpWordBoundary // matches word boundary `\b` OpNoWordBoundary // matches word non-boundary `\B` OpCapture // capturing subexpression with index Cap, optional name Name OpStar // matches Sub[0] zero or more times OpPlus // matches Sub[0] one or more times OpQuest // matches Sub[0] zero or one times OpRepeat // matches Sub[0] at least Min times, at most Max (Max == -1 is no limit) OpConcat // matches concatenation of Subs OpAlternate // matches alternation of Subs )
type Prog ¶
type Prog struct {
Inst []Inst
Start int // index of start instruction
NumCap int // number of InstCapture insts in re
}
A Prog is a compiled regular expression program.
func Compile ¶
Compile compiles the regexp into a program to be executed. The regexp should have been simplified already (returned from re.Simplify).
func (*Prog) Prefix ¶
Prefix returns a literal string that all matches for the regexp must start with. Complete is true if the prefix is the entire match.
type Regexp ¶
type Regexp struct {
Op Op // operator
Flags Flags
Sub []*Regexp // subexpressions, if any
Sub0 [1]*Regexp // storage for short Sub
Rune []rune // matched runes, for OpLiteral, OpCharClass
Rune0 [2]rune // storage for short Rune
Min, Max int // min, max for OpRepeat
Cap int // capturing index, for OpCapture
Name string // capturing name, for OpCapture
}
A Regexp is a node in a regular expression syntax tree.
func Parse ¶
Parse parses a regular expression string s, controlled by the specified Flags, and returns a regular expression parse tree. The syntax is described in the top-level comment for package regexp.
func (*Regexp) Simplify ¶
Simplify returns a regexp equivalent to re but without counted repetitions and with various other simplifications, such as rewriting /(?:a+)+/ to /a+/. The resulting regexp will execute correctly but its string representation will not produce the same parse tree, because capturing parentheses may have been duplicated or removed. For example, the simplified form for /(x){1,2}/ is /(x)(x)?/ but both parentheses capture as $1. The returned regexp may share structure with or be the original.
Source Files