Describes a series of alternatives (branches), a kleene star (*), or an optional element (?). More...
Source files:
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 | |
| 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, protected 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 | |
| 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) |
| override void | Call (PredVisitor visitor) |
| 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... | |
| Public Member Functions inherited from Loyc.ICloneable< Pred > | |
| T | Clone () |
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
◆ 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
◆ DefaultArm
| 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?)
◆ ErrorBranch
| 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.
◆ Greedy
| 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.
