Jeg lavede nedenstående som demo engang. Det har den fordel at det er kort, men den bagdel at det er meget rudimentært. 2-bogstav variabelnavne, så max 26 variable og den eneste datatype er int, de eneste operatorer er =, *, /, -, + og parenteser.
men måske den kan bruges som skelet til det du vil have :)
/*
** implement a very small interpreter
*/
import java.util.*;
import java.io.*;
class ParseError extends Exception {
public ParseError( String message ) {
super( message );
}
} // endclass ParseError
class RuntimeError extends Exception {
public RuntimeError( String message ) {
super( message );
}
} // endclass RuntimeError
interface Element { // the groups and atoms of a statement
public int getValue( ) throws RuntimeError;
public int setValue( int value ) throws RuntimeError;
} //end interface Element
class Value implements Element {
private int value;
public Value ( int value ) { this.value = value; }
public int getValue( ) throws RuntimeError {
return this.value;
}
public int setValue( int value ) throws RuntimeError {
throw new RuntimeError( "attempt to change the value of a constant." );
}
} //endclass Value
class Variable implements Element {
private static final Variable[] vt = new Variable[26]; // the nametable
private int value;
private boolean initialized;
private String name;
private Variable ( String name ) { // instances created only by getVariable()
this.initialized = false;
this.name = name;
}
static Variable getVariable( String name ) {
for ( int i=0; i<vt.length; i++ ) { // return existing variable
if ( vt[i] != null && vt[i].name.equals(name) ) return vt[i];
}
for ( int i=0; i<vt.length; i++ ) { // or create a new one
if ( vt[i] == null ) return ( vt[i] = new Variable( name ) );
}
throw new Error( "Impossible error. More that 26 variables used." );
}
public int getValue( ) throws RuntimeError {
if ( this.initialized ) return this.value;
throw new RuntimeError( "variable " +name +" not initialized." );
}
public int setValue( int value ) throws RuntimeError {
this.initialized = true;
return ( this.value = value );
}
} //endclass variable
class Triple implements Element {
private Element operand1, operand2;
private char operator;
public Triple ( Element op1, char operator, Element op2 ) {
this.operand1 = op1;
this.operator = operator;
this.operand2 = op2;
}
public int getValue() throws RuntimeError {
switch ( this.operator ) {
case '=': return operand1.setValue( operand2.getValue() );
case '+': return operand1.getValue() + operand2.getValue();
case '-': return operand1.getValue() - operand2.getValue();
case '*': return operand1.getValue() * operand2.getValue();
case '/': {
int divisor = operand2.getValue();
if ( divisor != 0 ) return operand1.getValue() / divisor;
throw new RuntimeError( "attempted division by 0.'" );
}
default:
throw new RuntimeError( "unknown operator code '" +operator +"'." );
}
}
public int setValue( int value ) throws RuntimeError {
throw new RuntimeError( "attempt to change the value of an expression." );
}
} // endclass Triple
// adds a one-token lookahead
class Tokenizer extends StringTokenizer {
String next;
public Tokenizer( String s ) {
super( s );
this.next = ( hasMoreTokens() ) ? nextToken() : " ";
}
char peekNextChar() {
return this.next.charAt(0);
}
boolean skipPredicted( String s ) {
if ( s.equals(next) ) {
this.next = ( hasMoreTokens() ) ? nextToken() : " ";
return true;
}
return false;
}
String fetchNext( ) {
String temp = this.next;
this.next = ( hasMoreTokens() ) ? nextToken() : " ";
return temp;
}
} // endclass Tokenizer
// inplement the simple syntax
class Compile {
static Tokenizer t;
static final String names = "ABCDEFGHIJKLMNOPQRSTUVWXUZ";
static final String digits = "0123456789";
static Element lValue() throws ParseError {
String name = t.fetchNext();
if ( names.indexOf(name) >= 0 ) return Variable.getVariable( name );
if ( digits.indexOf(name) >= 0 ) return new Value( Integer.parseInt( name ) );
throw new ParseError( "bad left side variable '" +name +"'." );
}
static Element parenthetical() throws ParseError {
Element temp = expression();
if ( t.skipPredicted(")") ) return temp;
throw new ParseError( "bad parenthetical, ')' expected." );
}
static Element factor() throws ParseError {
String nxt = t.fetchNext();
if ( nxt.equals( "(" ) ) return parenthetical();
if ( names.indexOf(nxt) >= 0 ) return Variable.getVariable( nxt );
if ( digits.indexOf(nxt) >= 0 ) return new Value( Integer.parseInt( nxt ) );
throw new ParseError( "Bad Factor at '" +nxt +"'." );
}
static Element term() throws ParseError {
Element op1 = factor();
char opr = t.peekNextChar();
while ( opr == '*' || opr == '/' ) {
t.fetchNext();
op1 = new Triple( op1, opr, factor() );
opr = t.peekNextChar();
}
return op1;
}
static Element expression() throws ParseError {
Element op1 = term();
char opr = t.peekNextChar();
while ( opr == '+' || opr == '-' ) {
t.fetchNext();
op1 = new Triple( op1, opr, term() );
opr = t.peekNextChar();
}
return op1;
}
static Element statement( String s ) {
t = new Tokenizer( s );
try {
Element op1 = lValue();
Element op2;
if ( t.skipPredicted("=") ) {
op2 = expression();
} else {
throw new ParseError( "no assignment in statement." );
}
if ( t.skipPredicted(";") ) return new Triple( op1, '=', op2 );
throw new ParseError( "missing ';' at end of statement." );
} catch ( ParseError e ) {
System.out.println( "error in line: " +s );
System.out.println( "Parsing error: " +e.getMessage() );
}
return new Value( -666 );
}
} // endclass Compile
// the main class compile and execute a file containing a simple program
class CalcFunction {
static final int MAX = 100; // max 100 statements
static Element[] statements = new Element[MAX];
static String[] lines = new String[MAX];
static int programLength = 0;
static String readLine( InputStream reader ) {
String line = "";
try {
int ch;
while ( (ch=reader.read()) != 13 && ch != -1 ) {
if ( ch != 10 ) line += (char)ch;
}
} catch ( Exception e ) {
System.out.print( "error in readLine." );
}
return line;
}
static void compile( String fileName ) {
FileInputStream fil;
try {
fil = new FileInputStream( fileName );
} catch ( Exception e ) {
System.out.print( "no such file found." );
throw new Error( "compilation terminated in error." );
}
String line = readLine( fil );
while ( ! ( line.equals("") ) ) {
lines[programLength] = line;
statements[ programLength++ ] = Compile.statement( line );
line = readLine( fil );
}
}
static void execute( ) {
for ( int i=0; i<programLength; i++ ) {
System.out.println( i +": " +lines[i] );
try {
System.out.println( " calculated value is " +statements[i].getValue() );
} catch ( RuntimeError e ) {
System.out.println ( "statement nr " +i +" failed: " +e.getMessage() );
}
}
}
public static void main( String[] args ) {
String fileName = "c:/testprogram.txt";
System.out.println( "\n--- Compiling '" +fileName +"'." );
compile( fileName );
System.out.println( "\n\n--- Running '" +fileName +"'." );
execute( );
}
} // endclass CalcFunction
/* file c:/testprogram.txt contain:
A = 5 ;
B = A * 2 + 9 ;
C = A + B * ( 1 - 1 ) ;
C = A + B / ( 1 - 1 ) ; // divide by zero
C = 7 + C ;
D = B + C + A * 2 ;
E = A * ( B + C ) ;
F = E / 5 ;
G = A + ( B + ( C + ( D + ( E + ( F * 2 ) ) ) ) ) ;
9 = 4 * A ; // assign to a number
*/
/* and gives the below output:
--- Compiling 'c:/testprogram.txt'.
error in line: 9 = 4 * A ;
Parsing error: bad left side variable '9'.
--- Running 'c:/testprogram.txt'.
0: A = 5 ; should give 5
calculated value is 5
1: B = A * 2 + 9 ; should give 19
calculated value is 19
2: C = A + B * ( 1 - 1 ) ;
calculated value is 5
3: C = A + B / ( 1 - 1 ) ;
statement nr 3 failed: attempted division by 0.'
4: C = 7 + C ;
calculated value is 12
5: D = B + C + A * 2 ;
calculated value is 41
6: E = A * ( B + C ) ;
calculated value is 155
7: F = E / 5 ;
calculated value is 31
8: G = A + ( B + ( C + ( D + ( E + ( F * 2 ) ) ) ) ) ;
calculated value is 294
9: 9 = 4 * A ;
calculated value is -666
Process Exit.
*/
mvh JakobA
Ny bruger
Nybegynder
Opret
Preview
