編譯器
範例 – 編譯數學運算式為中間碼
PS D:\ccc\book\aijs\code\07-language> node compileExp '3+2'
"3+2"
T0=3
T1=2
T2=T0+T1
PS D:\ccc\book\aijs\code\07-language> node compileExp '5*4/2'
"5*4/2"
T0=5
T1=4
T2=2
T3=T1/T2
T4=T0*T3
PS D:\ccc\book\aijs\code\07-language> node compileExp '3+(5*4)-2'
"3+(5*4)-2"
T0=3
T1=5
T2=4
T3=T1*T2
T4=2
T5=T3-T4
T6=T0+T5
原始碼 : compileExp.js
/* 運算式編譯器：
語法: E = T ([+-/*] E)*
T = N | (E)
範例：3+(5*4)-2 */
var c = console;
var tagMap={
N : ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"],
OP: ["+", "-", "*", "/"]
};
var wi = 0;
function isNext(tag) {
if (words[wi] === tag) return true;
var tagWords=tagMap[tag];
if (typeof tagWords === "undefined")
return false;
else
return (tagWords.indexOf(words[wi])>=0);
}
function next(tag) {
// c.log("tag="+tag+" word="+words[wi]);
if (isNext(tag)) {
return words[wi++];
}
throw Error("Error !");
}
var tempIdx = 0;
var getTemp=function() {
return tempIdx++;
}
// E = T ([+-/*] E)*
function E() {
var t = T();
while (isNext("OP")) {
var op = next("OP");
var e = E();
var result = getTemp();
console.log(" T%d=T%d%sT%d", result, t, op, e);
t = result;
}
return t;
}
// T = N | (E)
function T() {
if (isNext("N")) {
var t = getTemp();
var number = next("N");
console.log(" T%d=%d", t, number);
return t;
} else {
next("(");
var e = E();
next(")");
return e;
}
}
if (process.argv.length != 3) {
c.log("參數數量錯誤，請嘗試以下範例：\n\nnode compileExp '3+(5*4)-2'\n")
process.exit(1)
}
let words = process.argv[2]
c.log("%j", words);
E(words);