#line 5193 "lpsrc/elk.pak"
// useract.h see license.txt for copyright and terms of use
// interface to an object containing user-defined action functions
// the code appears in the .cc file generated by 'gramanl' from
// an associated .gr file
// the comments below are guidelines on writing grammar actions, since
// those grammar actions are composed to form the single-entry
// functions documented below
#ifndef USERACT_H
#define USERACT_H
#include "elk_glrconfig.h"
#include "sm_str.h"
#include "sm_srcloc.h"
class ParseTables; // parsetables.h
class FLX_RTL_EXTERN UserActions;
// user-supplied semantic values:
// - Semantic values are an arbitrary word, that the user can then
// use as a pointer or an integer or whatever. The parser
// generator inserts the appropriate casts, so the actual type
// I use here shouldn't ever be visible to the user.
// - Usually, SemanticValues that are used as pointers are considered
// to be owner pointers, but only in the sense that del() will be
// called. It's up to the user to decide if del() actually does
// anything.
typedef unsigned long SemanticValue;
// name of a null sval; can't use "NULL" because of __null weirdness in gcc-3...
#define NULL_SVAL 0
// package of functions; the user will create an instance of a class
// derived from this, and the parser will carry it along to invoke
// the various action functions
class FLX_RTL_EXTERN UserActions {
public:
// allow abstract user to delete
virtual ~UserActions();
// user-supplied reduction actions
// - production 'id' is being used to reduce
// - 'svals' contains an array of semantic values yielded by the RHS
// symbols, such that the 0th element is the leftmost RHS element;
// the pointers in the array are owner pointers (the array ptr itself
// is a serf)
// - 'loc' is the location of the left edge of the parse subtree
// - this fn returns the semantic value for the reduction; this return
// value is an owner pointer
typedef SemanticValue (*ReductionActionFunc)(
UserActions *context, // parser context class object
int productionId, // production being used to reduce
SemanticValue const *svals // array of semantic values
SOURCELOCARG( SourceLoc loc ) );
// get the actual function; two-step to avoid virtual call in inner loop
virtual ReductionActionFunc getReductionAction()=0;
// duplication of semantic values:
// - the given 'sval' is about to be passed to a reduction action
// function. the user must return a value to be stored in place
// of the old one, in case it is needed to pass to another action
// function in case of local ambiguity; 'sval' is a serf
// - the return value will be yielded (if necessary) to the next
// consumer action function, and is an owner ptr
// - some possible strategies:
// - return NULL, in which case it is probably an error for the
// value to be passed to another action (i.e. the grammar needs
// to be LALR(1) near this semantic value); in this case, 'del'
// will not be called on the NULL value
// - increment a reference count and return 'sval'
// - do nothing, and rely on some higher-level allocation scheme
// such as full GC, or regions
virtual SemanticValue duplicateTerminalValue(
int termId, SemanticValue sval)=0;
virtual SemanticValue duplicateNontermValue(
int nontermId, SemanticValue sval)=0;
// a semantic value didn't get passed to an action function, either
// because it was never used at all (e.g. a semantic value for a
// punctuator token, which the user can simply ignore), or because we
// duplicated it in anticipation of a possible local ambiguity, but
// then that parse turned out not to happen, so we're cancelling
// the dup now; 'sval' is an owner pointer
virtual void deallocateTerminalValue(int termId, SemanticValue sval)=0;
virtual void deallocateNontermValue(int nontermId, SemanticValue sval)=0;
// this is called when there are two interpretations for the same
// sequence of ground terminals, culminating in two different reductions
// deriving the same left-hand-side nonterminal (identified by 'ntIndex');
// it should return a value to be used in the place where they conflict'
// both 'left' and 'right' are owner pointers, and the return value
// is also an owner pointer
//
// NOTE: the 'left' value is always the node which came first, and
// might even have been yielded to another reduction already
// (depending on the grammar), whereas the 'right' value is always a
// node which was just created, and has definitely *not* been
// yielded to anything (this fact is critical to solving the general
// yield-then-merge problem)
virtual SemanticValue mergeAlternativeParses(
int ntIndex, SemanticValue left, SemanticValue right
SOURCELOCARG( SourceLoc loc )
)=0;
// after every reduction, the semantic value is passed to this function,
// which returns 'false' if the reduction should be cancelled; if it
// does return false, then 'sval' is an owner pointer (the parser engine
// will drop the value on the floor)
virtual bool keepNontermValue(int nontermId, SemanticValue sval)=0;
// every time a token is pulled from the lexer, this reclassifier is
// used to give the user a chance to reinterpret the token, before it
// is used for reduction lookahead comparisons; it returns the
// reclassified token type, or 'oldTokenType' to leave it unchanged
typedef int (*ReclassifyFunc)(UserActions *ths, int oldTokenType, SemanticValue sval);
// get the reclassifier
virtual ReclassifyFunc getReclassifier()=0;
// descriptions of symbols with their semantic values; this is useful
// for the ACTION_TRACE function of the parser
virtual sm_string terminalDescription(int termId, SemanticValue sval)=0;
virtual sm_string nonterminalDescription(int nontermId, SemanticValue sval)=0;
// get static names for all of the symbols
virtual char const *terminalName(int termId)=0;
virtual char const *nonterminalName(int termId)=0;
// get the parse tables for this grammar; the default action
// complains that no tables are defined
virtual ParseTables *makeTables();
};
// for derived classes, the list of functions to be declared
// (this macro is used by the generated code)
#define USER_ACTION_FUNCTIONS \
virtual ReductionActionFunc getReductionAction(); \
\
virtual SemanticValue duplicateTerminalValue( \
int termId, SemanticValue sval); \
virtual SemanticValue duplicateNontermValue( \
int nontermId, SemanticValue sval); \
\
virtual void deallocateTerminalValue( \
int termId, SemanticValue sval); \
virtual void deallocateNontermValue( \
int nontermId, SemanticValue sval); \
\
virtual SemanticValue mergeAlternativeParses( \
int ntIndex, SemanticValue left, SemanticValue right \
SOURCELOCARG( SourceLoc loc ) \
); \
\
virtual bool keepNontermValue(int nontermId, SemanticValue sval); \
\
virtual ReclassifyFunc getReclassifier(); \
\
virtual sm_string terminalDescription(int termId, SemanticValue sval); \
virtual sm_string nonterminalDescription(int nontermId, SemanticValue sval); \
\
virtual char const *terminalName(int termId); \
virtual char const *nonterminalName(int termId);
// a useraction class which has only trivial actions
class TrivialUserActions : public UserActions {
public:
USER_ACTION_FUNCTIONS
static SemanticValue doReductionAction(
UserActions *ths,
int productionId, SemanticValue const *svals
SOURCELOCARG( SourceLoc loc ) );
static int reclassifyToken(UserActions *ths,
int oldTokenType, SemanticValue sval);
};
#endif // USERACT_H
