removed leftover

recursiveDescentParsers/cplusplus/interpret++/interpreter.cpp

-// This code made available to his students by 
-// Prof. Ronald Moore  
-//     https://fbi.h-da.de/personen/ronald-moore/  
-//     mailto:ronald.moore@h-da.de
-// with no warranties whatsoever!
-
-
-#include <cassert>
-#include <cctype> // for isspace
-#include <cstdlib> // for strtod
-#include <iostream>
-#include <fstream>
-#include <string>
-// include <vector>
-
-// ===================
-// LEXICAL ANALYSIS
-// The following are taken to be tokens:
-// left and right parenthesis, the plus and minus characters,
-// as well as asterisk and forward slash -- and numbers.
-// In the script, substraction and division are not supported,
-// but it seems like time to add them.
-
-// Preliminaries and Utilities
-// ============================
-
-// Utility Types
-typedef double numberType; // feel fee to change this to something else like int or float or bigint....
-typedef enum Token { 
-	tok_number = 'n',
-	tok_lparen = '(',
-	tok_rparen = ')',
-	tok_plus   = '+',
-	tok_minus  = '-',
-	tok_times  = '*',
-	tok_div    = '/',
-	tok_eof    = 'E',
-	bad_tok    = 'X'
-} Token;
-
-// global variables -- sue me if you don't like that!
-static std::istream *input = &(std::cin); // until proven otherwise
-static std::string	currentLine( "" );
-static int	currentLineNumber = -1;
-static int	currentColumnNumber = 0;
-static int	currentTokenLength = 0;
-
-static Token next_token; // again with the global variables... 
-static numberType currentNumber; // = zero....
-
-static void printErrorMsg( const std::string Error )
-{
-	std::cout << "ERROR on line " << currentLineNumber
-	          << ", column " << currentColumnNumber << " : " 
-	          << Error << std::endl;
-	std::cout << currentLine;
-	for ( int col = 0; col < currentColumnNumber-1; col++ )
-		std::cout << '-';
-	std::cout << '^' << std::endl;
-} // end printErrorMsg
-
-// The Lexer
-// ==========
-static bool skippedWhiteSpace( ) { // return true if not at EOF, i.e. if skipped
-	while ( true ) {
-		int currentLineLength = currentLine.length();
-		while ( currentColumnNumber < currentLineLength )
-			if ( isspace( currentLine[ currentColumnNumber ] ) ) 
-				currentColumnNumber++;
-			else // if NOT isspace() 
-				return true;
-				
-		// if we're here, we're at the end of a line.
-		std::getline( *input, currentLine ); 
-		currentLineNumber++;
-		currentColumnNumber = 0;
-		if ( ! *input ) // EOF!!
-			return false;
-		// else, repeat! 
-		// Which is the same as 
-		// return skippedWhiteSpace()  -- i.e. tail recursion.
-	};
-};		
-
-static Token gettok( ) {
-	assert( input ); // we assume nullptr != input
-	if ( ! *input ) return bad_tok;
-	// else, we can read from input
-	
-	// Skip white space, going to next line as necessary
-	if ( ! skippedWhiteSpace( ) ) return tok_eof;
-	        
-	// We're have visible text in front of us.
-	char currentChar = currentLine[ currentColumnNumber ];
-	currentColumnNumber++; // usually, but see num...
-	switch (  currentChar ) {
-		case '(' : return tok_lparen;
-		case ')' : return tok_rparen;
-		case '+' : return tok_plus;
-		case '-' : return tok_minus;
-		case '*' : return tok_times;
-		case '/' : return tok_div;
-		default : 
-			// either we have a number in front of us, or we don't
-			assert( 0 < currentColumnNumber );
-			char *alpha = &(currentLine[ currentColumnNumber-1 ]);
-			// minus one because we incremented it before the switch
-			char *omega = nullptr; // until we call strtod...
-			double tmpValue = strtod( alpha, &omega );
-			if ( alpha == omega ) {
-				return bad_tok; // !!!
-			};
-			// else if strtod found a real number (or at least a double)
-			currentNumber = tmpValue; // let C++ do the converison
-			currentColumnNumber += (omega - alpha) -1;
-			// minus one because we incremented it before the switch
-			return tok_number;
-	
-	}; // end switch
-	assert( false ); // we should never get here!
-	return bad_tok;
-} // end gettok
-	
-// PARSING!!!
-// ===========
-// 
-// The grammar we are going to parse here is:
-// Grammar:
-// 	E	→ T E´
-// 	E´	→ + T E´  | - T E´ | ε
-// 	T	→ F T´
-// 	T´	→ * F T´  |  / F T´  |  ε
-// 	F	→ ( E ) | num
-// Note that the recursive descent function for (e.g.) E´ 
-// is nameded "E2ndHalf"-
-
-// Forward Declarations
-static numberType E();
-static numberType E2ndHalf();
-static numberType T();
-static numberType T2ndHalf();
-static numberType F();
-
-// 	E	→ T E´
-numberType E() { return T() + E2ndHalf(); }
-
-// 	T	→ F T´
-numberType T() { return F() * T2ndHalf(); }
-
-// 	E´	→ + T E´  | - T E´ | ε
-numberType E2ndHalf() {
-    switch ( next_token ) {
-		case tok_plus : 
-			next_token = gettok(); // eat +
-            return T() + E2ndHalf();
-
-		case tok_minus : 
-			next_token = gettok(); // eat -
-			return (-1.0 * T()) + E2ndHalf();
-
-		default : 
-			return 0.0;
-    }; 
-} // end E2ndHalf
-
-// 	T´	→ * F T´  |  / F T´  |  ε
-numberType  T2ndHalf() { 
-	numberType tmp, rhs, acc;
-    switch ( next_token ) {
-		case tok_times : 
-			next_token = gettok(); // eat *
-			return F() * T2ndHalf();
-    case tok_div : 
-		next_token = gettok(); // eat /
-		tmp = F();
-		if ( 0.0 != tmp ) 
-			return (1.0/tmp) * T2ndHalf();
-		// else if T() returned zero
-		printErrorMsg( "Division by zero!" );
-		// fall through to default return one
-        
-    default : 
-		return 1.0;
-    }; 
-} // end T2ndHalf
-
-// 	F	→ ( E ) | num
-numberType  F() {
-	numberType result = 0; 
-    switch ( next_token ) {
-		case tok_lparen : 
-			next_token = gettok(); // eat lparen
-            result = E();
-            if ( tok_rparen == next_token ) {
-				next_token = gettok(); // eat rparen
-                return result;
-			}; 
-			// else if rparen not found
-            printErrorMsg( "Expected Right Parenthesis" );
-            return 0.0;
-
-		case tok_number : 
-			result = currentNumber; // side-effect of last gettok() 
-            next_token = gettok(); // eat id
-            return result;
-
-		default : 
-			printErrorMsg( "Expected Left Parenthesis or number" );
-            return 0.0;
-    }; 
-}
-
-
-// main (!)
-// =========
-
-int main( int argc, char **argv ) {
-
-	if (2 != argc) {
-		std::cerr << "Usage: " << argv[0] << " <fileName>.\n" 
-		          << "You provided " << argc-1 << " arguments, we take exactly one (only).\n";
-		return( -1 );
-	};
-	// else if 1 == argc ....
-	std::string	fileName( argv[1] );
-	if ( "-" != fileName ) {
-		static std::ifstream ifs( fileName );
-		input = &ifs;
-	}
-
-	// Prime the pump!
-	next_token = gettok( );
-	
-	// get tokens and dump them... 
-	while ( tok_eof != next_token ) {
-		std::cout << currentLineNumber << ":" 
-		          << currentLine << std::endl;
-		numberType value = E( );
-		std::cout << "INTERPRETER: " << value << std::endl;
-	};
-	std::cout << "End Of File!" << std::endl;
-	
-	return 0; // Alles klar!!!
-}