tokeniser.ts

import { Token, TokenType } from "./Types";
import { isAlpha, isNumber, isNumericalLiteral, isFunction } from "./Utils";

export function tokenizer(expression: string): Token[] {
  let tokens: Token[] = [];
  let length: number = expression.length;
  let buffer: string = "";
  let count = 0;

  while (count < length) {
    let current: Token;

    switch (expression[count]) {
      case " ":
        count++;
        break;
      case "\t":
        count++;
        break;
      case "\n":
        count++;
        break;
      case "(":
        current = {
          type: TokenType.LeftParenthesis,
          value: expression[count],
        };
        tokens.push(current);
        count++;
        break;
      case ")":
        current = {
          type: TokenType.RightParenthesis,
          value: expression[count],
        };
        tokens.push(current);
        count++;
        break;
      case "+":
      case "%":
      case "/":
        current = {
          type: TokenType.Binary,
          value: expression[count],
        };
        tokens.push(current);
        count++;
        break;
      case "^":
        current = {
          type: TokenType.Binary,
          value: "**",
        };
        tokens.push(current);
        count++;
        break;
      case "*":
        if (expression[count + 1] == "*") {
          current = {
            type: TokenType.Binary,
            value: "**",
          };
          tokens.push(current);
          count += 2;
        } else {
          current = {
            type: TokenType.Binary,
            value: "*",
          };
          tokens.push(current);
          count++;
        }
        break;
      case "-":
        current = {
          type: TokenType.Minus,
          value: expression[count],
        };
        tokens.push(current);
        count++;
        break;
      case "!":
        current = {
          type: TokenType.Unary,
          value: expression[count],
        };
        tokens.push(current);
        count++;
        break;
      default:
        if (isNumber(expression[count])) {
          while (isNumber(expression[count])) {
            buffer += expression[count];
            count++;
          }
          let current = {
            type: TokenType.Number,
            value: buffer,
          };
          tokens.push(current);
          buffer = "";
        } else if (isAlpha(expression[count])) {
          while (isAlpha(expression[count])) {
            buffer += expression[count];
            count++;
          }
          if (isFunction(buffer)) {
            current = {
              type: TokenType.Unary,
              value: buffer,
            };
          } else if (buffer == "pi") {
            current = {
              type: TokenType.Number,
              value: Math.PI.toString(),
            };
          } else {
            throw new Error(`Unknown operation: ${buffer}`);
          }

          tokens.push(current);
          buffer = "";
        } else count++;
    }
  }
  return tokens;
}