serene-simple/src/main/java/serene/simple/Reader.java

/**
 * Serene (simple) - A PoC lisp to collect data on Serenes concepts
 * Copyright (C) 2019-2020 Sameer Rahmani <lxsameer@gnu.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA  02110-1301, USA.
 */
package serene.simple;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackReader;
import java.util.ArrayList;
import java.util.List;


public class Reader {
  public static Node readNode(PushbackReader inputStream) throws IOException, IllegalArgumentException, SereneException {
    char c = (char) inputStream.read();
    inputStream.unread(c);

    if (c == '(') {
      return readList(inputStream);
    }
    else if (Character.isDigit(c)) {
      return readNumber(inputStream);
    }
    else if (c == '"') {
      return readString(inputStream);
    }
    else if (c == ')') {
      throw new IllegalArgumentException("Unmatch paranthesis.");
    }
    else {
      return readSymbol(inputStream);
    }
  }

  public static ListNode<Node> read(InputStream inputStream) throws IOException, IllegalArgumentException, SereneException {
    return read(new PushbackReader(new InputStreamReader(inputStream)));
  }

  public static ListNode<Node> read(PushbackReader inputStream) throws IOException, IllegalArgumentException, SereneException {
    List<Node> nodes = new ArrayList<Node>();
    skipWhiteSpaces(inputStream);

    char c = (char) inputStream.read();
    while ((byte) c != -1) {
      if (c == ';') {
        break;
      }

      inputStream.unread(c);
      nodes.add(readNode(inputStream));
      skipWhiteSpaces(inputStream);
      c = (char) inputStream.read();
    }

    return ListNode.list(nodes);
  }

  private static Node readList(PushbackReader inputStream) throws IOException, SereneException {
    char opening = (char) inputStream.read();
    assert opening == '(' : "Lists must start with a '('";

    List<Node> nodes = new ArrayList<Node>();

    do {
      skipWhiteSpaces(inputStream);
      char c = (char) inputStream.read();

      if (c == ')') {
        break;
      } else if ((byte) c == -1) {
        throw new EOFException("EOF reached before closing of list");
      } else {
        inputStream.unread(c);
        nodes.add(readNode(inputStream));
      }
    } while(true);

    return SpecialForm.check(ListNode.list(nodes));
  }

  private static Node readSymbol(PushbackReader inputStream) throws IOException {
    String str = "";

    while (true) {
      int ch = inputStream.read();

      if(isWhiteSpace(ch) || isClosingChar(ch) || ch == -1) {
        inputStream.unread(ch);
        break;
      };
      str = str + (char) ch;
    }

    switch(str) {
    case "true":
      return new TrueNode();
    case "false":
      return new FalseNode();
    case "nil":
      return new NilNode();
    default:
      return new SymbolNode(str);
    }

  }

  private static Node readNumber(PushbackReader inputStream) throws IOException {
    int ch = inputStream.read();
    String number = "";

    while (Character.isDigit((char) ch)) {
      number = number + (char) ch;
      ch = inputStream.read();
    }

    inputStream.unread(ch);
    return new NumberNode(Long.parseLong(number, 10));
  }

  private static Node readString(PushbackReader inputStream) throws IOException {
    char opening = (char) inputStream.read();
    assert opening == '"' : "Strings should start with '\"'";
    String str = "";

    while (true) {
      char ch = (char) inputStream.read();

      if(ch == '"') {
        break;
      }
      str = str + ch;
    };

    return new StringNode(str);
  }

  private static char readAndIgnoreComments(PushbackReader inputStream) throws IOException {
    char firstChar = (char) inputStream.read();

    if (firstChar == ';') {
      while(true) {
        char ch = (char) inputStream.read();

        if(ch == -1 || ch == '\n') {
          break;
        }
      }
      return readAndIgnoreComments(inputStream);
    }
    else {
      return firstChar;
    }
  }

  private static void skipWhiteSpaces(PushbackReader inputStream) throws IOException {
    int ch = inputStream.read();

    while (isWhiteSpace(ch)) {
      ch = inputStream.read();
    }
    inputStream.unread(ch);
  }

  private static boolean isWhiteSpace(int ch) {
    return (ch == ' ' || ch == '\t' || ch == '\f' || ch == '\r' || ch == '\n');
  }

  private static boolean isClosingChar(int ch) {
    return (ch == ')' || ch == ']' ||
            ch == '}');
  }
}