usr/share/doc/bison/examples/mfcalc/calc.h

/* Function type.  */
typedef double (*func_t) (double);



/* Data type for links in the chain of symbols.  */
struct symrec
{
  char *name;  /* name of symbol */
  int type;    /* type of symbol: either VAR or FNCT */
  union
  {
    double var;      /* value of a VAR */
    func_t fnctptr;  /* value of a FNCT */
  } value;
  struct symrec *next;  /* link field */
};



typedef struct symrec symrec;

/* The symbol table: a chain of 'struct symrec'.  */
extern symrec *sym_table;

symrec *putsym (char const *, int);
symrec *getsym (char const *);