Struct AlangCursor

Represents a cursor for parsing Alang expressions from an input string.

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 a string input. The input string is never modified. Instead, the cursor maintains a lightweight span of the remaining input. The parser in the Automata.Core.Alang namespace only needs to create a single cursor instance that is passed along during the parse process. The contract of the AlangCursor is that it always points to a non-white-space character or EOI if the input is empty.

Consequently:

- All methods in AlangCursor that move the cursor must ensure on exit that leading whitespace is trimmed.

- All methods in AlangCursor can assume on entry that the input is trimmed of leading whitespace.

Constructors

AlangCursor(string)

Represents a cursor for parsing Alang expressions from an input string.

Declaration

public AlangCursor(string input)

Parameters

Type	Name	Description
string	input	The input string to parse.

Remarks

A cursor is a lightweight struct that consumes characters from the left of a string input. The input string is never modified. Instead, the cursor maintains a lightweight span of the remaining input. The parser in the Automata.Core.Alang namespace only needs to create a single cursor instance that is passed along during the parse process. The contract of the AlangCursor is that it always points to a non-white-space character or EOI if the input is empty.

Consequently:

- All methods in AlangCursor that move the cursor must ensure on exit that leading whitespace is trimmed.

- All methods in AlangCursor can assume on entry that the input is trimmed of leading whitespace.

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

ConsumeAtom()

Consumes an Atom from the input.

Declaration

public Atom ConsumeAtom()

Returns

Type	Description
Atom	The consumed Atom.

Remarks

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

ConsumeRightParen()

Consumes a right parenthesis (RightParen) from the input, advancing the cursor.

Declaration

public void ConsumeRightParen()

Exceptions

Type	Condition
AlangFormatException	Thrown when the next character is not a right parenthesis.

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.

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.

TryConsumeDifferenceOperator()

Tries to consume a difference operator (Difference) from the input and advances the cursor if successful.

Declaration

public bool TryConsumeDifferenceOperator()

Returns

Type	Description
bool	true iff the difference operator was successfully consumed.

TryConsumeIntersectionOperator()

Tries to consume an intersection operator (Intersection) from the input and advances the cursor if successful.

Declaration

public bool TryConsumeIntersectionOperator()

Returns

Type	Description
bool	true iff the intersection operator was successfully consumed.

TryConsumeLeftParen()

Tries to consume a left parenthesis (LeftParen) from the input and advances the cursor if successful.

Declaration

public bool TryConsumeLeftParen()

Returns

Type	Description
bool	true iff the left parenthesis was successfully consumed.

TryConsumeUnionOperator()

Tries to consume a union operator (Union) from the input and advances the cursor if successful.

Declaration

public bool TryConsumeUnionOperator()

Returns

Type	Description
bool	true iff the union operator was successfully consumed.