/****************************************************//* File: parse.c                                    *//* The parser implementation for the TINY compiler  *//* Compiler Construction: Principles and Practice   *//* Kenneth C. Louden                                *//****************************************************/#include "globals.h"#include "util.h"#include "scan.h"#include "parse.h"static TokenType token; /* holds current token *//* function prototypes for recursive calls */static TreeNode * stmt_sequence(void);static TreeNode * statement(void);static TreeNode * if_stmt(void);static TreeNode * repeat_stmt(void);static TreeNode * assign_stmt(void);static TreeNode * read_stmt(void);static TreeNode * write_stmt(void);static TreeNode * exp(void);static TreeNode * simple_exp(void);static TreeNode * term(void);static TreeNode * factor(void);static void syntaxError(char * message){ fprintf(listing,"\n>>> ");  fprintf(listing,"Syntax error at line %d: %s",lineno,message);  Error = TRUE;}static void match(TokenType expected){ if (token == expected) token = getToken();  else {    syntaxError("unexpected token -> ");    printToken(token,tokenString);    fprintf(listing,"      ");  }}TreeNode * stmt_sequence(void){ TreeNode * t = statement();  TreeNode * p = t;  while ((token!=ENDFILE) && (token!=END) &&         (token!=ELSE) && (token!=UNTIL))  { TreeNode * q;    match(SEMI);    q = statement();    if (q!=NULL) {      if (t==NULL) t = p = q;      else /* now p cannot be NULL either */      { p->sibling = q;        p = q;      }    }  }  return t;}TreeNode * statement(void){ TreeNode * t = NULL;  switch (token) {    case IF : t = if_stmt(); break;    case REPEAT : t = repeat_stmt(); break;    case ID : t = assign_stmt(); break;    case READ : t = read_stmt(); break;    case WRITE : t = write_stmt(); break;    default : syntaxError("unexpected token -> ");              printToken(token,tokenString);              token = getToken();              break;  } /* end case */  return t;}TreeNode * if_stmt(void){ TreeNode * t = newStmtNode(IfK);  match(IF);  if (t!=NULL) t->child[0] = exp();  match(THEN);  if (t!=NULL) t->child[1] = stmt_sequence();  if (token==ELSE) {    match(ELSE);    if (t!=NULL) t->child[2] = stmt_sequence();  }  match(END);  return t;}TreeNode * repeat_stmt(void){ TreeNode * t = newStmtNode(RepeatK);  match(REPEAT);  if (t!=NULL) t->child[0] = stmt_sequence();  match(UNTIL);  if (t!=NULL) t->child[1] = exp();  return t;}TreeNode * assign_stmt(void){ TreeNode * t = newStmtNode(AssignK);  if ((t!=NULL) && (token==ID))    t->attr.name = copyString(tokenString);  match(ID);  match(ASSIGN);  if (t!=NULL) t->child[0] = exp();  return t;}TreeNode * read_stmt(void){ TreeNode * t = newStmtNode(ReadK);  match(READ);  if ((t!=NULL) && (token==ID))    t->attr.name = copyString(tokenString);  match(ID);  return t;}TreeNode * write_stmt(void){ TreeNode * t = newStmtNode(WriteK);  match(WRITE);  if (t!=NULL) t->child[0] = exp();  return t;}TreeNode * exp(void){ TreeNode * t = simple_exp();  if ((token==LT)||(token==EQ)) {    TreeNode * p = newExpNode(OpK);    if (p!=NULL) {      p->child[0] = t;      p->attr.op = token;      t = p;    }    match(token);    if (t!=NULL)      t->child[1] = simple_exp();  }  return t;}TreeNode * simple_exp(void){ TreeNode * t = term();  while ((token==PLUS)||(token==MINUS))  { TreeNode * p = newExpNode(OpK);    if (p!=NULL) {      p->child[0] = t;      p->attr.op = token;      t = p;      match(token);      t->child[1] = term();    }  }  return t;}TreeNode * term(void){ TreeNode * t = factor();  while ((token==TIMES)||(token==OVER))  { TreeNode * p = newExpNode(OpK);    if (p!=NULL) {      p->child[0] = t;      p->attr.op = token;      t = p;      match(token);      p->child[1] = factor();    }  }  return t;}TreeNode * factor(void){ TreeNode * t = NULL;  switch (token) {    case NUM :      t = newExpNode(ConstK);      if ((t!=NULL) && (token==NUM))        t->attr.val = atoi(tokenString);      match(NUM);      break;    case ID :      t = newExpNode(IdK);      if ((t!=NULL) && (token==ID))        t->attr.name = copyString(tokenString);      match(ID);      break;    case LPAREN :      match(LPAREN);      t = exp();      match(RPAREN);      break;    default:      syntaxError("unexpected token -> ");      printToken(token,tokenString);      token = getToken();      break;    }  return t;}/****************************************//* the primary function of the parser   *//****************************************//* Function parse returns the newly  * constructed syntax tree */TreeNode * parse(void){ TreeNode * t;  token = getToken();  t = stmt_sequence();  if (token!=ENDFILE)    syntaxError("Code ends before file\n");  return t;}