Struct AlangCursor

Represents a cursor for parsing Alang regex strings.

Inherited Members

ValueType.Equals(object)

ValueType.GetHashCode()

object.Equals(object, object)

object.GetType()

object.ReferenceEquals(object, object)

Namespace: Automata.Core.Alang

Assembly: Automata.Core.dll

Syntax

public ref struct AlangCursor

Remarks

A cursor is a lightweight struct that consumes characters from the left of the input regexString as it is parsed. For performance, regexString is never split, copied or modified. Instead, the cursor maintains a lightweight span of the remaining regex string. Also, the parser in the Automata.Core.Alang namespace only needs to maintain a single cursor instance through the entire parse process. The contract of the AlangCursor is that it always points to a non-white-space character or EOI if the regex string is empty.

Consequently:

- All methods in AlangCursor that move the cursor must ensure on exit that leadingwhitespace is skipped.

- All methods in AlangCursor can assume on entry that the cursor points to a non-whitespace character.

This struct is also the sole point for throwing all types of parsing exceptions. These are handled by the methods prefixed by Should.

Constructors

AlangCursor(string)

Represents a cursor for parsing Alang regex strings.

Declaration

public AlangCursor(string regexString)

Parameters

Type	Name	Description
string	regexString	The regex string to parse.

Remarks

A cursor is a lightweight struct that consumes characters from the left of the input regexString as it is parsed. For performance, regexString is never split, copied or modified. Instead, the cursor maintains a lightweight span of the remaining regex string. Also, the parser in the Automata.Core.Alang namespace only needs to maintain a single cursor instance through the entire parse process. The contract of the AlangCursor is that it always points to a non-white-space character or EOI if the regex string is empty.

Consequently:

- All methods in AlangCursor that move the cursor must ensure on exit that leadingwhitespace is skipped.

- All methods in AlangCursor can assume on entry that the cursor points to a non-whitespace character.

This struct is also the sole point for throwing all types of parsing exceptions. These are handled by the methods prefixed by Should.

Properties

CursorIndex

Current position of the cursor in the original input string.

Declaration

public readonly int CursorIndex { get; }

Property Value

Type	Description
int

IsEmpty

Indicates whether the cursor has reached the end of the input.

Declaration

public readonly bool IsEmpty { get; }

Property Value

Type	Description
bool

IsExpressionStart

Indicates whether the current character indicates the start of an expression. false if the input is empty.

Declaration

public readonly bool IsExpressionStart { get; }

Property Value

Type	Description
bool

NextAsString

String representation of the next character in the input, or "End-Of-Input" if at the end of the input.

Declaration

public readonly string NextAsString { get; }

Property Value

Type	Description
string

Methods

ConsumeSymbol()

Consumes an Symbol from the input.

Declaration

public Symbol ConsumeSymbol()

Returns

Type	Description
Symbol	The consumed Symbol.

Remarks

This method will return an empty (invalid) Symbol if no characters could be consumed. It is up to the calling code to handle this.

Is(char)

Indicates whether the first character in the remaining input is the specified character.

Declaration

public readonly bool Is(char c)

Parameters

Type	Name	Description
char	c	The character to check.

Returns

Type	Description
bool	true iff the first character is the specified character.

IsNot(char)

Indicates whether the first character in the remaining input is not the specified character.

Declaration

public readonly bool IsNot(char c)

Parameters

Type	Name	Description
char	c	The character to check.

Returns

Type	Description
bool	true iff the first character is NOT the specified character.

ShouldBeRightOperand(char)

Validates that there is right operand after a binary operator.

Declaration

public readonly void ShouldBeRightOperand(char binaryOperator)

Parameters

Type	Name	Description
char	binaryOperator	The preceding binary operator character. (Only used for better informed error messages if validation fails).

Exceptions

Type	Condition
AlangFormatException	Thrown when the current character is not a right parenthesis ')'.

ShouldBeRightParen()

Validates that the current character is a right parenthesis.

Declaration

public readonly void ShouldBeRightParen()

Exceptions

Type	Condition
AlangFormatException	Thrown when the current character is not a right parenthesis ')'.

ShouldNotBeEmpty()

Validates that the cursor is not at the end of input.

Declaration

public readonly void ShouldNotBeEmpty()

Remarks

This method enforces the rule that empty input is not valid in Alang expressions. To represent an empty set, use parentheses '()' instead.

Exceptions

Type	Condition
AlangFormatException	Thrown when the cursor is at the end of input.

ShouldNotBeOperator()

Validates that the current character is not an operator.

Declaration

public readonly void ShouldNotBeOperator()

Remarks

This method ensures expressions do not start with an operator.

Exceptions

Type	Condition
AlangFormatException	Thrown when the current character is an operator.

ShouldNotBeRightParen()

Validates that the current character is not a right parenthesis.

Declaration

public readonly void ShouldNotBeRightParen()

Exceptions

Type	Condition
AlangFormatException	Thrown when the current character is a right parenthesis ')'.

ToString()

String representation of the remaining input.

Declaration

public override readonly string ToString()

Returns

Type	Description
string	A string that represents the remaining input.

Overrides

ValueType.ToString()

TryConsume(char)

Tries to consume the specified character from the input and advances the cursor if successful.

Declaration

public bool TryConsume(char c)

Parameters

Type	Name	Description
char	c	The character to attempt to consume.

Returns

Type	Description
bool	true iff the character was successfully consumed.

TryConsumeAny(params char[])

Tries to consume one of the specified characters from the input and advances the cursor if successful.

Declaration

public char TryConsumeAny(params char[] chars)

Parameters

Type	Name	Description
char[]	chars	An array of characters to attempt to consume.

Returns

Type	Description
char	The character that was consumed if successful; otherwise, Invalid.

Remarks

This method supports inclusion of EOI to also match against End-Of-Input.

TryConsumeBinaryOperator(char)

Tries to consume a binary operator from the input and advances the cursor if successful.

Declaration

public bool TryConsumeBinaryOperator(char binaryOperator)

Parameters

Type	Name	Description
char	binaryOperator	The binary operator character to attempt to consume.

Returns

Type	Description
bool	true iff the binary operator was successfully consumed and the next character is a valid expression start.

Exceptions

Type	Condition
AlangFormatException	Thrown when the binary operator was consumed but the next character was not IsExpressionStart .