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Chapter 3. Using Bison > An Improved Calculator That Creates ASTs
3.5. An Improved Calculator That Creates ASTs
This example is big enough to be worth dividing into several source files, so we’ll put most of the C code into a separate file, which means we also need a C header file to declare the routines and data structures used in the various files (Example 3-1).
Example 3-1. Calculator that builds an AST: header fb3-1.h
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* Declarations for a calculator fb3-1
*/
/* interface to the lexer */
extern int yylineno; /* from lexer */
void yyerror(char *s, ...);
/* nodes in the abstract syntax tree */
struct ast {
int nodetype;
struct ast *l;
struct ast *r;
};
struct numval {
int nodetype; /* type K for constant */
double number;
};
/* build an AST */
struct ast *newast(int nodetype, struct ast *l, struct ast *r);
struct ast *newnum(double d);
/* evaluate an AST */
double eval(struct ast *);
/* delete and free an AST */
void treefree(struct ast *);
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