Package java_cup
Class production
java.lang.Object
java_cup.production
- Direct Known Subclasses:
action_production
This class represents a production in the grammar. It contains
a LHS non terminal, and an array of RHS symbols. As various
transformations are done on the RHS of the production, it may shrink.
As a result a separate length is always maintained to indicate how much
of the RHS array is still valid.
I addition to construction and manipulation operations, productions provide methods for factoring out actions (see remove_embedded_actions()), for computing the nullability of the production (i.e., can it derive the empty string, see check_nullable()), and operations for computing its first set (i.e., the set of terminals that could appear at the beginning of some string derived from the production, see check_first_set()).
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected action_part
An action_part containing code for the action to be performed when we reduce with this production.protected static Hashtable
Table of all productions.protected terminal_set
First set of the production.protected int
Index number of the production.protected symbol_part
The left hand side non-terminal.protected boolean
Nullability of the production (can it derive the empty string).protected boolean
Is the nullability of the production known or unknown?protected int
Count of number of reductions using this production.protected production_part[]
A collection of parts for the right hand side.protected int
How much of the right hand side array we are presently using.protected static int
Static counter for assigning unique index numbers. -
Constructor Summary
ConstructorsConstructorDescriptionproduction
(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l) Constructor with no action string.production
(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, String action_str) Full constructor. -
Method Summary
Modifier and TypeMethodDescriptionaction()
An action_part containing code for the action to be performed when we reduce with this production.protected String
action_translate
(String act_string, int act_pos, Hashtable label_map, Hashtable label_types) Translate all the label names within an action string to appropriate code.static Enumeration
all()
Access to all productions.Update (and return) the first set based on current NT firsts.boolean
Check to see if the production (now) appears to be nullable.boolean
equals
(production other) Equality comparison.boolean
Generic equality comparison.First set of the production.int
hashCode()
Produce a hash code.int
index()
Index number of the production.protected static boolean
is_id_char
(char c) Determine if a character can be in a label id.protected static boolean
is_id_start
(char c) Determine if a given character can be a label id starter.protected String
label_translate
(String id_str, int act_pos, Hashtable label_map, Hashtable label_types) Determine the translation for one label id found within a code_string.lhs()
The left hand side non-terminal.protected int
merge_adjacent_actions
(production_part[] rhs_parts, int len) Helper routine to merge adjacent actions in a set of RHS partsvoid
Increment the count of reductions with this non-terminalboolean
nullable()
Nullability of the production (can it derive the empty string).boolean
Is the nullability of the production known or unknown?int
Count of number of reductions using this production.static int
number()
Total number of productions.protected void
Remove all embedded actions from a production by factoring them out into individual action production using new non terminals.rhs
(int indx) Access to the collection of parts for the right hand side.int
How much of the right hand side array we are presently using.protected action_part
strip_trailing_action
(production_part[] rhs_parts, int len) Helper routine to strip a trailing action off rhs and return itConvert to a simpler string.toString()
Convert to a string.protected String
translate_labels
(production_part[] rhs, int rhs_len, String final_action, String lhs_type) Translate label names to appropriate code within all action strings.
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Field Details
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_all
Table of all productions. Elements are stored using their index as the key. -
next_index
protected static int next_indexStatic counter for assigning unique index numbers. -
_lhs
The left hand side non-terminal. -
_rhs
A collection of parts for the right hand side. -
_rhs_length
protected int _rhs_lengthHow much of the right hand side array we are presently using. -
_action
An action_part containing code for the action to be performed when we reduce with this production. -
_index
protected int _indexIndex number of the production. -
_num_reductions
protected int _num_reductionsCount of number of reductions using this production. -
_nullable_known
protected boolean _nullable_knownIs the nullability of the production known or unknown? -
_nullable
protected boolean _nullableNullability of the production (can it derive the empty string). -
_first_set
First set of the production. This is the set of terminals that could appear at the front of some string derived from this production.
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Constructor Details
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production
public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, String action_str) throws internal_error Full constructor. This constructor accepts a LHS non terminal, an array of RHS parts (including terminals, non terminals, and actions), and a string for a final reduce action. It does several manipulations in the process of creating a production object. After some validity checking it translates labels that appear in actions into code for accessing objects on the runtime parse stack. It them merges adjacent actions if they appear and moves any trailing action into the final reduce actions string. Next it removes any embedded actions by factoring them out with new action productions. Finally it assigns a unique index to the production.Factoring out of actions is accomplished by creating new "hidden" non terminals. For example if the production was originally:
A ::= B {action} C D
then it is factored into two productions:A ::= B X C D X ::= {action}
(where X is a unique new non terminal). This has the effect of placing all actions at the end where they can be handled as part of a reduce by the parser.- Throws:
internal_error
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production
public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l) throws internal_error Constructor with no action string.- Throws:
internal_error
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Method Details
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all
Access to all productions. -
number
public static int number()Total number of productions. -
lhs
The left hand side non-terminal. -
rhs
Access to the collection of parts for the right hand side.- Throws:
internal_error
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rhs_length
public int rhs_length()How much of the right hand side array we are presently using. -
action
An action_part containing code for the action to be performed when we reduce with this production. -
index
public int index()Index number of the production. -
num_reductions
public int num_reductions()Count of number of reductions using this production. -
note_reduction_use
public void note_reduction_use()Increment the count of reductions with this non-terminal -
nullable_known
public boolean nullable_known()Is the nullability of the production known or unknown? -
nullable
public boolean nullable()Nullability of the production (can it derive the empty string). -
first_set
First set of the production. This is the set of terminals that could appear at the front of some string derived from this production. -
is_id_start
protected static boolean is_id_start(char c) Determine if a given character can be a label id starter.- Parameters:
c
- the character in question.
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is_id_char
protected static boolean is_id_char(char c) Determine if a character can be in a label id.- Parameters:
c
- the character in question.
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label_translate
protected String label_translate(String id_str, int act_pos, Hashtable label_map, Hashtable label_types) Determine the translation for one label id found within a code_string. Symbols appearing in the RHS correspond to objects found on the parse stack at runtime. The code to access them, becomes code to access an object at the appropriate offset from the top of the stack, and then cast that to the proper type.- Parameters:
id_str
- the name of the id to be translated.act_pos
- the original position of the action it appears in.label_map
- a hash table mapping labels to positions in the RHS.type_map
- a hash table mapping labels to declared symbol types.
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action_translate
protected String action_translate(String act_string, int act_pos, Hashtable label_map, Hashtable label_types) Translate all the label names within an action string to appropriate code.- Parameters:
act_string
- the string to be translatedact_pos
- the position that the action originally held in the production.label_map
- a hash table mapping labels to positions in the RHS.type_map
- a hash table mapping labels to declared symbol types.
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translate_labels
protected String translate_labels(production_part[] rhs, int rhs_len, String final_action, String lhs_type) Translate label names to appropriate code within all action strings.- Parameters:
rhs
- array of RHS parts.rhs_len
- how much of rhs to consider valid.final_action
- the final action string of the production.lhs_type
- the object type associated with the LHS symbol.
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merge_adjacent_actions
Helper routine to merge adjacent actions in a set of RHS parts- Parameters:
rhs_parts
- array of RHS parts.len
- amount of that array that is valid.- Returns:
- remaining valid length.
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strip_trailing_action
Helper routine to strip a trailing action off rhs and return it- Parameters:
rhs_parts
- array of RHS parts.len
- how many of those are valid.- Returns:
- the removed action part.
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remove_embedded_actions
Remove all embedded actions from a production by factoring them out into individual action production using new non terminals. if the original production was:A ::= B {action1} C {action2} D
then it will be factored into:A ::= B NT$1 C NT$2 D NT$1 ::= {action1} NT$2 ::= {action2}
where NT$1 and NT$2 are new system created non terminals.- Throws:
internal_error
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check_nullable
Check to see if the production (now) appears to be nullable. A production is nullable if its RHS could derive the empty string. This results when the RHS is empty or contains only non terminals which themselves are nullable.- Throws:
internal_error
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check_first_set
Update (and return) the first set based on current NT firsts. This assumes that nullability has already been computed for all non terminals and productions.- Throws:
internal_error
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equals
Equality comparison. -
equals
Generic equality comparison. -
hashCode
public int hashCode()Produce a hash code. -
toString
Convert to a string. -
to_simple_string
Convert to a simpler string.- Throws:
internal_error
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