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function forth(print = console.log) {
const s = []; // the stack
const popNum = () => Number(s.pop());
const fs = {
'/' : () => {
const a2 = popNum();
const a1 = popNum();
s.push(a1 / a2);
},
'-' : () => {
const a2 = popNum();
const a1 = popNum();
s.push(a1 - a2);
},
'+' : () => { s.push(popNum() + popNum()) },
'*' : () => { s.push(popNum() * popNum()) },
'=' : () => { s.push(popNum() === popNum()) },
'then' : () => {/*Doing nothing skips the token*/},
'if' : (initialIdx, tokens) => {
if (!s.pop()) {
let localIdx = initialIdx;
while (tokens[localIdx] && tokens[localIdx] !== 'then') {localIdx++}
return localIdx - initialIdx;
}
},
'not' : () => { s.push(!s.pop()) },
'.' : () => { print(s.pop()) },
'peek' : () => { print(s[s.length - 1]) },
'dup' : () => { s.push(s[s.length - 1]) },
':' : (initialIdx, tokens) => {
let localIdx = initialIdx + 1;
const fname = tokens[localIdx++];
const fnContent = [];
for (;tokens[localIdx] !== ';'; localIdx++) {
fnContent.push(tokens[localIdx]);
}
fs[fname] = () => {
exec(fnContent);
}
return localIdx - initialIdx; // numItemsSkipped
},
's' : () => print(JSON.stringify(s)),
'sum' : () => {
let total = 0;
while (s.length > 0) {
total += popNum();
}
s.push(total);
},
'(' : (initialIdx, tokens) => {
let localIdx = initialIdx + 1;
while (tokens[localIdx] !== ')') { localIdx++ }
return localIdx - initialIdx;
}
}
function exec(tokens) {
for (let tokenIdx = 0; tokenIdx < tokens.length; tokenIdx++) {
const token = tokens[tokenIdx];
if (fs[token]) {
const numItemsSkipped = fs[token](tokenIdx, tokens);
if (Number.isInteger(numItemsSkipped)) {
tokenIdx += numItemsSkipped;
}
}
else {
s.push(token);
}
}
}
return t =>
new Promise(
resolve => {
exec(t.split(/[ \n\t]+/).filter(x => x !== ''));
resolve();
}
);
}
/*
root tag to add to page:
<div id="forthroot"></div>
* */
if (typeof window !== 'undefined') { // browser UI
const style = document.createElement('style')
style.innerHTML = `
#forthroot * {
background-color: #42456f;
color: white;
font-family: monospace;
font-size: 1.2rem;
box-sizing: border-box;
}
#forthouter {
cursor: text;
border: solid thin black;
}
#forthline {
width: 97%;
border: none;
}
#forthline:focus {
outline: none;
}
#forthresultsbox {
height: 90vh;
}
#forthresults {
height: 100%;
margin-top: 0px;
overflow: clip;
margin: 0px;
}
#forthlinelabel {
padding-top:1px;
max-width: 3%;
}
#forthform {
margin-bottom: 0px;
}
`;
document.head.appendChild(style);
forthroot.innerHTML = `
<div id="forthouter">
<form id="forthform">
<label id="forthlinelabel" for="forthline" position="left">></label>
<input id="forthline" type="text" value="" autocomplete="off">
</form>
<div id='forthresultsbox'>
<pre id="forthresults"></pre>
</div>
</div>`
forthouter.onclick = () => forthline.focus();
const print = x => { forthresults.innerHTML = x + '\n' + forthresults.innerHTML; };
const m = forth(print);
forthform.onsubmit = () => {
const input = forthline.value;
if (input !== '') {
m(input).then(() => print(`> ${input}`));
forthline.value = '';
}
return false;
}
} else { // UI if NodeJS
const readline = require('readline');
const rl = readline.createInterface({ input: process.stdin, output: process.stderr });
const prompt = (query) => new Promise((resolve) => rl.question(query, resolve));
const m = forth();
(async () => {
while (true) {
const input = await prompt("> ");
m(input)
}
})();
}
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