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JS Code from Building a Basic Interpreter, '80s Style Part 2
const tokens = ["CLS", "PRINT", ":" ];
function tokenize(inStr) {
let out = []; // return value is "crunched" array
let idx = 0; // index into inStr
let ch = ""; // current character
while (idx < inStr.length) {
ch = inStr.charCodeAt(idx); // get the current character code
if (ch >= 48 && ch <= 57) { // NUMERIC LITERAL
out.push (0xFD);
const numberLiteralStr = inStr.substr(idx).match(/^[\d|A-F|a-f|x|X]+/)[0];
idx += numberLiteralStr.length;
const numberLiteral = Number(numberLiteralStr);
const bytes = new Uint8Array(new Uint16Array([numberLiteral]).buffer);
out.push(...bytes)
continue;
}
if (ch === 34) { // STRING LITERAL
out.push (0xFB); // string-in-code token
const stringLiteral = inStr.substr(idx+1).match(/^[^"]*/)[0];
idx += stringLiteral.length+1;
out.push(...Array.from(stringLiteral, ch => ch.charCodeAt(0)));
idx++; // go past the quote
out.push(0); // end of string
continue;
}
if (ch === 32) { // collapse SPACEs
const allTheSpaces = inStr.substr(idx).match(/^\ +/)[0];
idx += allTheSpaces.length;
out.push(ch);
continue;
}
const tokenMatch = tokens.findIndex(token => inStr.substr(idx).startsWith(token));
if (tokenMatch > -1) {
out.push(tokenMatch + 128);
idx += tokens[tokenMatch].length;
continue;
}
const variableMatch = inStr.substr(idx).match(/^[A-Z]+[A-Z0-9]*[\$]*/); console.log(variableMatch);
if (variableMatch) {
out.push(0xFA);
const variableName = variableMatch[0];
const variableIndexName = variableName.substr(0,2);
const variableType = variableName.endsWith("$") ? "string" : "number";
let variableIndex;
if (variableIndexName.length === 1) {
variableIndex = variableIndexName.charCodeAt(0) - 65;
} else {
variableIndex = 27 + (variableIndexName.charCodeAt(0) - 65) * 36 + variableIndexName.charCodeAt(1);
}
variableIndex += {"number": 0b0000_0000_0000_0000, "string": 0b1000_0000_0000_0000}[variableType];
const hiByte = (variableIndex & 0xFF00) >> 8;
const loByte = (variableIndex & 0x00FF);
out.push(hiByte, loByte);
out.push(variableName.length);
out.push(...Array.from(variableName, ch => ch.charCodeAt(0)));
idx += variableName.length;
continue;
}
out.push(ch);
idx++;
}
out.push(0); // NUL
return out;
}
const toHex = arr => arr.map(val => val.toString(16).toUpperCase().padStart(2,"0")).join(" ");
console.log(toHex(tokenize(`PRINT ZZ 96 0xFF "Hi"`)))
console.log(toHex(tokenize(`CLS: PRINT "Hello, World"`)))
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