http://compilers.iecc.com/crenshaw/tutor9.txt

top-down-design-impl.cpp

#include <iostream>
#include <string>
using namespace std;

/* *
 * <program> ::= <program-header> <block> '.'
 * <program-header> ::= PROGRAM <ident>
 * <block> ::= <declarations> <statements>
 * */

char Look;

void Expected(const string& str) {
	cout << "Expected " << str << endl;
	exit(-1);
}

void GetChar() {
	Look = getchar();
}

// Match a specific character
void Match(char ch) {
	if (ch == Look) {
		GetChar();
	}
	else {
		Expected((string)("") + ch);
	}
}

char GetName() {
	if (!isalpha(Look)) {
		Expected("Name");
	}
	char ch = toupper(Look);
	GetChar();
	return ch;
}

// Post a Label to Output
void PostLabel(const string& label) {
	cout << label << ":" << endl;
}

// Write the Prolog
void Prolog() {
	cout << "WARMST EQU $A01E" << endl;
}

// Write the Epilog
void Epilog(char Name) {
	cout << "DC WARMST" << endl;
	cout << "END " << Name << endl;
}

/* *
 * <declarations> ::= ( <label list> 	|
 * 			<constant list> |
 * 			<type list>	|
 * 			<variable list> |
 * 			<procedure>	|
 * 			<function>	)*
 * */
/* Process Label Statement */
void Labels() {
	Match('l');
}
/* Process Const Statement */
void Constants() {
	Match('c');
}
/* Process Type Statement */
void Types() {
	Match('t');
}
/* Process Var Statement */
void Variables() {
	Match('v');
}
/* Process Procedure Definition */
void DoProcedure() {
	Match('p');
}
/* Process Function Definition */
void DoFunction() {
	Match('f');
}
// Parse and Translate the Declarations Part
void Declarations() {
	bool check = true;
	while (check) {
		switch (Look) {
			case 'l': Labels(); break;
			case 'c': Constants(); break;
			case 't': Types(); break;
			case 'v': Variables(); break;
			case 'p': DoProcedure(); break;
			case 'f': DoFunction(); break;
			default: check = false; break;
		}
	}
}

/*
 * <statements> ::= <compound statement>
 * <compound statement> ::= BEGIN <statement>
 * 				(';' <statement>) END
 * <statement> ::= <simple statement> | <structured statement>
 * <simple statement> ::= <assignment> | <procedure call> | null
 * <structured statement> ::= <compound statement>	|
 * 			      <if statement>		|
 * 			      <case statement>		|
 * 			      <while statement>		|
 * 			      <repeat statement>	|
 * 			      <for statement>		|
 * 			      <with statement>
 * */
 /* Parse and Translate the Statement Part */
void Statements() {
	Match('b');
	while (Look != 'e') {
		GetChar();
	}
	Match('e');
}

// Parse and Translate a Pascal block
void DoBlock(char Name) {
	Declarations();
	PostLabel((string)"" + Name);
	Statements();
}

// Parse and Translate A Program
void Prog() {
	char Name;
	
	Match('p');	// Handles program header part
	Name = GetName();
	Prolog();
	DoBlock(Name);
	Match('.');
	Epilog(Name);
}

void Init() {
	GetChar();
}

int main() {
	Init();
	Prog();
	return 0;
}