Renamed package 'greg' to 'regex'
This commit is contained in:
200
regex/postfixNode.go
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200
regex/postfixNode.go
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package regex
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import "fmt"
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type NodeType int
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// This is a slice containing all escapable characters that have special meaning.
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// Eg. \b is word boundary, \w is word character etc.
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var escapedChars []rune = []rune("wWdDbBnaftrvsS0")
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// This is a list of the possible node types
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const (
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CHARACTER NodeType = iota
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CHARCLASS
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PIPE
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CONCATENATE
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KLEENE
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QUESTION
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PLUS
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ASSERTION
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LPAREN
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RPAREN
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)
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// Helper constants for lookarounds
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const POSITIVE = 1
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const NEGATIVE = -1
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const LOOKAHEAD = 1
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const LOOKBEHIND = -1
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var INFINITE_REPS int = -1 // Represents infinite reps eg. the end range in {5,}
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// This represents a node in the postfix representation of the expression
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type postfixNode struct {
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nodetype NodeType
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contents []rune // Contents of the node
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startReps int // Minimum number of times the node should be repeated - used with numeric specifiers
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endReps int // Maximum number of times the node should be repeated - used with numeric specifiers
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allChars bool // Whether or not the current node represents all characters (eg. dot metacharacter)
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except []postfixNode // For inverted character classes, we match every unicode character _except_ a few. In this case, allChars is true and the exceptions are placed here.
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lookaroundSign int // ONLY USED WHEN nodetype == ASSERTION. Whether we have a positive or negative lookaround.
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lookaroundDir int // Lookbehind or lookahead
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nodeContents []postfixNode // ONLY USED WHEN nodetype == CHARCLASS. Holds all the nodes inside the given CHARCLASS node.
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}
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// Converts the given list of postfixNodes to one node of type CHARCLASS.
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// Used to convert eg. 'a', 'b' and 'c' to '[abc]'.
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// If the character class is negated, it returns a postfixNode of type CHARACTER.
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// This node will behave like the dot metacharacter, but it has a longer list of runes that
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// it will not match.
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func newCharClassNode(nodes []postfixNode, negated bool) postfixNode {
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rtv := postfixNode{}
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rtv.nodetype = CHARCLASS
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rtv.startReps = 1
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rtv.endReps = 1
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if negated {
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rtv.nodetype = CHARACTER
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rtv.contents = []rune{ANY_CHAR}
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rtv.allChars = true
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rtv.except = nodes
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} else {
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rtv.nodeContents = nodes
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}
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return rtv
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}
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// Creates a new escaped node - the given character is assumed to have been preceded by a backslash
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func newEscapedNode(c rune, inCharClass bool) (postfixNode, error) {
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toReturn := postfixNode{}
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toReturn.startReps = 1
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toReturn.endReps = 1
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switch c {
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case 's': // Whitespace
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, whitespaceChars...)
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case 'S': // Non-whitespace
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toReturn = newPostfixDotNode()
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toReturn.except = append([]postfixNode{}, newPostfixNode(whitespaceChars...))
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case 'd': // Digits
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, digitChars...)
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case 'D': // Non-digits
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toReturn = newPostfixDotNode()
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toReturn.except = append([]postfixNode{}, newPostfixNode(digitChars...))
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case 'w': // word character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, wordChars...)
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case 'W': // Non-word character
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toReturn = newPostfixDotNode()
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toReturn.except = append([]postfixNode{}, newPostfixNode(wordChars...))
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case 'b', 'B':
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if c == 'b' && inCharClass {
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(8))
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} else {
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toReturn.nodetype = ASSERTION
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toReturn.contents = append(toReturn.contents, c)
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}
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case 'n': // Newline character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, '\n')
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case '0': // NULL character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(0))
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case 'a': // Bell character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(7))
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case 'f': // Form feed character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(12))
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case 't': // Horizontal tab character
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(9))
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case 'r': // Carriage return
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(13))
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case 'v': // Vertical tab
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, rune(11))
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case '-': // Literal hyphen - only in character class
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if inCharClass {
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, '-')
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} else {
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return postfixNode{}, fmt.Errorf("invalid escape character")
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}
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default: // None of the above - append it as a regular character
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if isNormalChar(c) { // Normal characters cannot be escaped
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return postfixNode{}, fmt.Errorf("invalid escape character")
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}
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, c)
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}
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return toReturn, nil
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}
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// Creates and returns a postfixNode based on the given contents
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func newPostfixNode(contents ...rune) postfixNode {
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if len(contents) < 1 {
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panic("Empty node.")
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}
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to_return := postfixNode{}
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to_return.startReps = 1
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to_return.endReps = 1
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if len(contents) > 1 { // If the node has more than element, it must be a character class - the type must be CHARACTER
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to_return.nodetype = CHARACTER
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to_return.contents = contents
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} else { // Node has one element, could be anything
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switch contents[0] {
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case '+':
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to_return.nodetype = PLUS
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case '?':
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to_return.nodetype = QUESTION
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case '*':
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to_return.nodetype = KLEENE
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case '|':
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to_return.nodetype = PIPE
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case CONCAT:
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to_return.nodetype = CONCATENATE
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case '^', '$':
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to_return.nodetype = ASSERTION
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case '(':
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to_return.nodetype = LPAREN
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case ')':
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to_return.nodetype = RPAREN
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default:
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to_return.nodetype = CHARACTER
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}
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to_return.contents = append(to_return.contents, contents...)
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// Special cases for LPAREN and RPAREN - they have special characters defined for them
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if to_return.nodetype == LPAREN {
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to_return.contents = []rune{LPAREN_CHAR}
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}
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if to_return.nodetype == RPAREN {
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to_return.contents = []rune{RPAREN_CHAR}
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}
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}
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return to_return
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}
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// Creates and returns a postfixNode representing the 'dot' metacharacter.
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func newPostfixDotNode() postfixNode {
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toReturn := postfixNode{}
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toReturn.startReps = 1
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toReturn.endReps = 1
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toReturn.nodetype = CHARACTER
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toReturn.allChars = true
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toReturn.contents = []rune{ANY_CHAR}
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return toReturn
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}
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// Creates a character node, regardless of the contents
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func newPostfixCharNode(contents ...rune) postfixNode {
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toReturn := postfixNode{}
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toReturn.startReps = 1
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toReturn.endReps = 1
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toReturn.nodetype = CHARACTER
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toReturn.contents = append(toReturn.contents, contents...)
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return toReturn
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}
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