用antlr制作计算器 [英] making calculator with antlr
问题描述
我对使用 antlr 非常陌生.我正在制作一个计算器，我已经制作了我的语法.如果我使用侦听器而不是访问者，是否可以获得结果?我不知道这是否有意义，但我正在使用侦听器，我唯一能做的就是让它打印出输入而不是输入的计算结果.我在网上查过，每个例子都使用了访问者.那么我应该使用访问者还是在使用侦听器时可以得到结果?我希望这是有道理的.
am very new to using antlr. I am making a calculator and I have already made my grammar. is it possible to get results if I use listener instead of visitor? I don't know if that makes sense but I am using the listener and the only thing I have been able to do is to get it to print out the input but not the calculated result from the input. I have checked online and every example uses the visitor. so should I use visitor or is there someway you can get results when using listener? I hope that makes sense.
这是我的 g4 文件
grammar calc;
TYPE_INT: 'int';
TYPE_FLOAT: 'float';
EQU: '=';
MUL: '*';
DIV: '/';
PLU: '+';
MIN: '-';
L_BKT: '(';
R_BKT: ')';
WRITE: 'write';
END_MARK: ';';
ID: ([A-Z]|[a-z]) ([A-Z]|[a-z]|[0-9])*;
INT: ('0'|([1-9]([0-9])*));
FLOAT: ('0'|([1-9]([0-9])*))'.'([0-9]+)(('e'|'E')('+'|'-')?('0'|([1-9]([0-
9])*)))? ;
WS : [ \t\r\n]+ -> skip ;
declare: (typeInt=TYPE_INT|typeFloat=TYPE_FLOAT) id=ID;
assign: id=ID equ=EQU expr;
expr: expr (plu=PLU|min=MIN) expr2|expr2;
expr2: expr2 (mul=MUL|div=DIV) expr3 |expr3;
expr3: floatNumber=FLOAT| intNumber=INT| id=ID| lBkt=L_BKT expr rBkt=R_BKT;
writeFunction: write=WRITE lBkt=L_BKT id=ID rBkt=R_BKT;
stmt: declare| assign| writeFunction;
stmts: (stmt endMark=END_MARK)*;
r: stmts;
这是我在 calcbaseListener 中使用的 variable 和 variableList 类
this is the variable and variableList class I made to use in calcbaseListener
public class Variable {
public String name="";
public String type="int";
public float value=(float) 0.0;
}
public class VariableList {
List<Variable> list=new ArrayList();
private static VariableList self=new VariableList();
public static VariableList getList(){
return self;
}
public Variable find(String name){
Variable v=null;
for(int i=0;i<list.size();i++){
Variable tmp=list.get(i);
if(tmp.name.equals(name)){
v=tmp;
}
}
return v;
}
public void add(Variable v){
list.add(v);
}
}
这是我放在 calcBaseListener 中的代码
this is the code I put in calcBaseListener
public void exitDeclare(calcParser.DeclareContext ctx) {
String name=ctx.id.getText();
Variable v=new Variable();
v.name = name;
if(ctx.typeFloat != null) {
v.type = "float";
} else {
v.type = "int";
}
VariableList list = VariableList.getList();
if(list.find(v.name) == null) {
list.add(v);
} else {
System.out.println("The id has already been declared");
System.exit(0);
}
}
public void exitAssign(calcParser.AssignContext ctx) {
String name = ctx.id.getText();
VariableList list = VariableList.getList();
if(list.find(name) == null) {
System.out.println("Undeclared id");
System.exit(0);
} else {
Variable v = list.find(name);
if(v.type.equals(ctx.expr().v.type) || v.type.equals("float") &&
ctx.expr().v.type.equals("int")) {
v.value = ctx.expr().v.value;
}
else {
System.out.println("The type of int assigned to the type of type
of float error");
System.exit(0);
}
}
}
public void exitExpr(calcParser.ExprContext ctx) {
if(ctx.expr()==null){
if(ctx.v.type.equals(ctx.expr2().v.type)||
ctx.v.type.equals("float")&&ctx.expr2().v.type.equals("int")){
ctx.v.value=ctx.expr().v.value;
}else{
System.out.println("The type of int assign to the tpye of float
error");
System.exit(0);
}
ctx.v.value=ctx.expr().v.value;
return;
}
if(ctx.plu!=null){
String type="";
if(ctx.expr().v.type.equals("float")
||ctx.expr2().v.type.equals("float")){
type="float";
}else{
type="int";
}
if(ctx.v.type.equals(type)||
ctx.v.type.equals("float")&&type.equals("int")){
ctx.v.value=ctx.expr().v.value;
}else{
System.out.println("The type of int assign to the tpye of float
error");
System.exit(0);
}
ctx.v.value=ctx.expr().v.value+ctx.expr2().v.value;
return;
}
if(ctx.min!=null){
String type="";
if(ctx.expr().v.type.equals("float")
||ctx.expr2().v.type.equals("float")){
type="float";
}else{
type="int";
}
if(ctx.v.type.equals(type)||
ctx.v.type.equals("float")&&type.equals("int")){
ctx.v.value=ctx.expr().v.value;
}else{
System.out.println("The type of int assign to the tpye of float
error");
System.exit(0);
}
ctx.v.value=ctx.expr().v.value-ctx.expr2().v.value;
return;
}
}
public void exitExpr2(calcParser.Expr2Context ctx) {
if(ctx.expr2()==null){
if(ctx.v.type.equals(ctx.expr3().v.type)||
ctx.v.type.equals("float")&&ctx.expr3().v.type.equals("int")){
ctx.v.value=ctx.expr2().v.value;
}else{
System.out.println("The type of int assign to the tpye of float error");
System.exit(0);
}
ctx.v.value=ctx.expr2().v.value;
return;
}
if(ctx.mul!=null){
String type="";
if(ctx.expr2().v.type.equals("float")
||ctx.expr3().v.type.equals("float")){
type="float";
}else{
type="int";
}
if(ctx.v.type.equals(type)||
ctx.v.type.equals("float")&&type.equals("int")){
ctx.v.value=ctx.expr2().v.value;
}else{
System.out.println("The type of int assign to the tpye of float error");
System.exit(0);
}
ctx.v.value=ctx.expr2().v.value*ctx.expr3().v.value;
return;
}
if(ctx.div!=null){
String type="";
if(ctx.expr2().v.type.equals("float")
||ctx.expr3().v.type.equals("float")){
type="float";
}else{
type="int";
}
if(ctx.v.type.equals(type)||
ctx.v.type.equals("float")&&type.equals("int")){
ctx.v.value=ctx.expr2().v.value;
}else{
System.out.println("The type of int assign to the tpye of float error");
System.exit(0);
}
ctx.v.value=ctx.expr2().v.value/ctx.expr3().v.value;
return;
}
}
public void exitExpr3(calcParser.Expr3Context ctx) {
if(ctx.floatNumber!=null){
ctx.v.type="float";
ctx.v.value=Float.valueOf(ctx.floatNumber.getText());
}
if(ctx.intNumber!=null){
ctx.v.type="int";
ctx.v.value=Float.valueOf(ctx.intNumber.getText());
}
if(ctx.id!=null){
VariableList list=VariableList.getList();
String name=ctx.id.getText();
ctx.v.type=list.find(name).type;
ctx.v.value=list.find(name).value;
}
if(ctx.expr()!=null){
ctx.v.type=ctx.expr().v.type;
ctx.v.value=ctx.expr().v.value;
}
}
public void exitWriteFunction(calcParser.WriteFunctionContext ctx) {
VariableList list=VariableList.getList();
String name=ctx.id.getText();
if(list.find(name)!=null){
Variable v=list.find(name);
System.out.println(v.value);
}else{
System.out.println("Undecleared id");
System.exit(0);
}
}
如果我像这样编写代码，是否有可能获得计算值?
is it possible for me to get value of a calculation if i write my code like this?
推荐答案
为了回答您的原始问题:是的，可以使用侦听器来实现计算器.
In order to answer your orignal question: Yes it is possible to implement a calculator using a listener.
此时将简单地参考 这个 GitHub 存储库，它提供了两个:一个使用侦听器的实现一个使用访问者.
At this point will simply refer to this GitHub repository that provides both: One implementation using a listener and one using a visitor.
由于上面引用的语法无法处理分配，我建议看看这个 repo 也确实提供了除纯算术解析之外的赋值功能.但请注意，该方法没有利用 ANTLR 处理直接左递归的能力，这会导致为同一任务产生更多代码.
As the above referenced grammar can't handle assignments I'D suggest to have a look at this repo as well that does provide the assignment-functionality next to the pure arithmetic-parsing. Note though that this one does not take advantage of ANTLR's capability to deal with direct left-recursion which leads to a lot more code for the same task.
总的来说，我建议您利用直接左递归规则，因为这样会使您的语法更易于阅读.结合替代规则标签，这是一个真正强大的功能.
In general I'd advise you to do take advantage of direct left-recursive rules as tehy make your grammar a lot simpler to read. In combination alternative-rule-labeling it's a real powerful feature.
这篇关于用antlr制作计算器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
