Loyc.LLParserGenerator.Alts Class Reference

Describes a series of alternatives (branches), a kleene star (*), or an optional element (?). More...

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Source file:

• /Main/LLLPG/RuleAndPreds/Predicates.cs

Inheritance diagram for Loyc.LLParserGenerator.Alts:

Remarks

Describes a series of alternatives (branches), a kleene star (*), or an optional element (?).

Branches, stars and optional elements are represented by the same class because they all require prediction, and prediction works the same way for all three.

The one-or-more operator '+' is represented simply by repeating the contents once, i.e. (x+) is converted to (x x*), which is a Seq of two elements: x and an Alts object that contains a clone of x (a clone, because a Pred object can only exist in one place in a grammar). Thus, there is no predicate that represents x+ itself.

Alts has a few options beyond the LoopMode:

• A greedy flag (applies to loops only)
• An optional default branch number (DefaultArm)
• An optional error branch (ErrorBranch), which may be set to the DefaultErrorBranch.Value, and a ExitOnError flag
• NoAmbigWarningFlags represents use of / rather than |

I have an uneasy feeling that the code in here is overly complicated, particularly the way I handled slashes and merging Alts. I'm just not sure what simpler techniques I should have used instead.

Public fields
LoopMode	Mode = LoopMode.None
bool	Greedy = null
	Specifies whether the loop is greedy or nongreedy (ignored for non-loops). This flag is used in case of ambiguity between between the arms and exit branch; if the loop is greedy, the arms win; if not, loop exits. More...
List< Pred >	Arms = new List<Pred>()
Pred	ErrorBranch = null
	Specifies the action to take for error input. If an error branch is specified, it serves as the default arm and DefaultArm has no significant effect. If ErrorBranch is null but DefaultArm is null and the LLParserGenerator.NoDefaultArm flag is set, a default error handler is generated. More...
bool	ExitOnError = true
int	DefaultArm = null
	Specifies the case that should be encoded as the default in the prediction tree, i.e., the else clause in the if-else chain or the "default:" label in the switch statement. More...
Public fields inherited from Loyc.LLParserGenerator.Pred
LNode	PreAction
LNode	PostAction
Symbol	VarLabel
bool	VarIsList
Func< LNode, LNode >	ResultSaver
	A function that saves the result produced by the matching code of this predicate (null if the result is not saved). For example, if the parser generator is given the predicate @[ x='a'..'z' ], the default matching code will be @(Match('a', 'z')), and ResultSaver will be set to a function that receives this matching code and returns @(x = Match('a', 'z')) in response. More...

Properties
IEnumerable< Pred >	ArmsAndCustomErrorBranch [get]
bool	HasExit [get]
int	ArmCountPlusExit [get]
override bool	IsNullable [get]
Properties inherited from Loyc.LLParserGenerator.Pred
LNode	Basis [get, set]
abstract bool	IsNullable [get]
	Returns true if this predicate can match an empty input. More...
object	Location [get]
Properties inherited from Loyc.IHasLocation
object	Location [get]

Public Member Functions
override void	Call (PredVisitor visitor)
	Alts (LNode basis, LoopMode mode, bool?greedy=null)
	Alts (LNode basis, LoopMode mode, Pred contents, bool?greedy=null)
bool	HasErrorBranch (LLParserGenerator llpg)
bool	HasDefaultErrorBranch (LLParserGenerator llpg)
bool	NonExitDefaultArmRequested ()
override Pred	Clone ()
	Deep-clones a predicate tree. Terminal sets and Nodes referenced by the tree are not cloned; the clone's value of Next will be null. The same Pred cannot appear in two places in a tree, so you must clone before re-use. More...
override string	ToString ()
string	AltName (int altNum)
Public Member Functions inherited from Loyc.LLParserGenerator.Pred
	Pred (LNode basis)
LNode	AutoSaveResult (LNode matchingCode)
string	ToStringWithPosition ()
virtual string	ChooseGotoLabel ()
	Optional. If this predicate represents the matching code for a branch of an Alts and this code is reached through a goto statement, this method is used to select a label name. Supported by RuleRef. More...

Static Public Member Functions
static Alts	Merge (LNode basis, Pred a, Pred b, bool slashJoined, BranchMode aMode, BranchMode bMode, IMessageSink warnings)
Static Public Member Functions inherited from Loyc.LLParserGenerator.Pred
static Seq	operator+ (char a, Pred b)
static Seq	operator+ (Pred a, char b)
static Seq	operator+ (Pred a, Pred b)
static Pred	operator| (char a, Pred b)
static Pred	operator| (Pred a, char b)
static Pred	operator| (Pred a, Pred b)
static Pred	operator/ (Pred a, Pred b)
static Pred	operator+ (Pred a)
static Pred	Or (Pred a, Pred b, bool slashJoined)
static Pred	Or (Pred a, Pred b, bool slashJoined, LNode basis, BranchMode aMode=BranchMode.None, BranchMode bMode=BranchMode.None, IMessageSink sink=null)
static Alts	Star (Pred contents, bool?greedy=null)
static Alts	Opt (Pred contents, bool?greedy=null)
static Seq	Plus (Pred contents, bool?greedy=null)
static TerminalPred	Range (char lo, char hi)
static TerminalPred	Set (IPGTerminalSet set)
static TerminalPred	Set (string set)
static TerminalPred	Set (params LNode[] s)
static TerminalPred	Not (params LNode[] s)
static TerminalPred	Char (char c)
static TerminalPred	Chars (params char[] c)
static Seq	Seq (string s, LNode basis=null)
static Rule	Rule (string name, Pred pred, bool isStartingRule=false, bool isToken=false, int maximumK=-1)
static Pred	operator+ (LNode pre, Pred p)
static Pred	operator+ (Pred p, LNode post)
static LNode	MergeActions (LNode action, LNode action2)
static AndPred	And (object test)
static AndPred	AndNot (object test)
static Pred	Set (string varName, Pred pred)
static Pred	SetVar (string varName, Pred pred)
static Pred	AddSet (string varName, Pred pred)
static Pred	Op (string varName, Symbol @operator, Pred pred)

Member Function Documentation

override Pred Loyc.LLParserGenerator.Alts.Clone ( )

inlinevirtual

Deep-clones a predicate tree. Terminal sets and Nodes referenced by the tree are not cloned; the clone's value of Next will be null. The same Pred cannot appear in two places in a tree, so you must clone before re-use.

Reimplemented from Loyc.LLParserGenerator.Pred.

References Loyc.LLParserGenerator.Alts.Clone().

Referenced by Loyc.LLParserGenerator.Alts.Clone().

Member Data Documentation

int Loyc.LLParserGenerator.Alts.DefaultArm = null

Specifies the case that should be encoded as the default in the prediction tree, i.e., the else clause in the if-else chain or the "default:" label in the switch statement.

Use 0 for the first arm (only warning messages add 1 to arm indexes). -1 means that the exit branch is the default (if there is no exit branch, the last branch is the default instead?)

Pred Loyc.LLParserGenerator.Alts.ErrorBranch = null

Specifies the action to take for error input. If an error branch is specified, it serves as the default arm and DefaultArm has no significant effect. If ErrorBranch is null but DefaultArm is null and the LLParserGenerator.NoDefaultArm flag is set, a default error handler is generated.

bool Loyc.LLParserGenerator.Alts.Greedy = null

Specifies whether the loop is greedy or nongreedy (ignored for non-loops). This flag is used in case of ambiguity between between the arms and exit branch; if the loop is greedy, the arms win; if not, loop exits.

Greedy == null by default. This means that the loop is still greedy, but a warning is printed if ambiguity is detected.