Rewrite the parsing interfaces in Kotlin.

core/src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java

@@ -124,7 +124,7 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
      * @param matches the list of tokens from the source string.
      * @return the construct tree expression.
      */
-    public TreeNode constructRecursive(List<Match<TokenType>> matches) {
+    public TreeNode constructRecursive(List<? extends Match<TokenType>> matches) {
         if (matches.size() == 0) throw new ParseException("no tokens left in input");
         Match<TokenType> match = matches.remove(0);
         TokenType matchType = match.getType();
@@ -172,7 +172,7 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
     }
 
     @Override
-    public TreeNode constructTree(List<Match<TokenType>> tokens) {
+    public TreeNode constructTree(List<? extends Match<TokenType>> tokens) {
         if (tokens.isEmpty()) throw new ParseException("no input tokens");
         tokens = intoPostfix(new ArrayList<>(tokens));
         Collections.reverse(tokens);

core/src/main/java/org/nwapw/abacus/parsing/Tokenizer.java

@@ -1,20 +0,0 @@
-package org.nwapw.abacus.parsing;
-
-import java.util.List;
-
-/**
- * Interface that provides the ability to convert a string into a list of tokens.
- *
- * @param <T> the type of the tokens produced.
- */
-public interface Tokenizer<T> {
-
-    /**
-     * Converts a string into tokens.
-     *
-     * @param string the string to convert.
-     * @return the list of tokens, or null on error.
-     */
-    public List<T> tokenizeString(String string);
-
-}

core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java

@@ -1,48 +0,0 @@
-package org.nwapw.abacus.parsing;
-
-import org.nwapw.abacus.tree.TreeNode;
-
-import java.util.List;
-
-/**
- * TreeBuilder class used to piece together a Tokenizer and
- * Parser of the same kind. This is used to essentially avoid
- * working with any parameters at all, and the generics
- * in this class are used only to ensure the tokenizer and parser
- * are of the same type.
- *
- * @param <T> the type of tokens created by the tokenizer and used by the parser.
- */
-public class TreeBuilder<T> {
-
-    /**
-     * The tokenizer used to convert a string into tokens.
-     */
-    private Tokenizer<T> tokenizer;
-    /**
-     * The parser used to parse a list of tokens into a tree.
-     */
-    private Parser<T> parser;
-
-    /**
-     * Create a new Tree Builder with the given tokenizer and parser
-     *
-     * @param tokenizer the tokenizer to turn strings into tokens
-     * @param parser    the parser to turn tokens into a tree
-     */
-    public TreeBuilder(Tokenizer<T> tokenizer, Parser<T> parser) {
-        this.tokenizer = tokenizer;
-        this.parser = parser;
-    }
-
-    /**
-     * Parse the given string into a tree.
-     *
-     * @param input the string to parse into a tree.
-     * @return the resulting tree.
-     */
-    public TreeNode fromString(String input) {
-        return parser.constructTree(tokenizer.tokenizeString(input));
-    }
-
-}

core/src/main/kotlin/org/nwapw/abacus/parsing/Parser.kt

@@ -1,16 +1,17 @@
-package org.nwapw.abacus.parsing;
+package org.nwapw.abacus.parsing
 
-import org.nwapw.abacus.tree.TreeNode;
-
-import java.util.List;
+import org.nwapw.abacus.tree.TreeNode
 
 /**
- * An itnerface that provides the ability to convert a list of tokens
+ * Converter from tokens into a parse tree.
+ *
+ * An interface that provides the ability to convert a list of tokens
  * into a parse tree.
  *
  * @param <T> the type of tokens accepted by this parser.
  */
-public interface Parser<T> {
+
+interface Parser<in T> {
 
     /**
      * Constructs a tree out of the given tokens.
@@ -18,5 +19,6 @@ public interface Parser<T> {
      * @param tokens the tokens to construct a tree from.
      * @return the constructed tree, or null on error.
      */
-    public TreeNode constructTree(List<T> tokens);
-}
+    fun constructTree(tokens: List<T>): TreeNode
+
+}

core/src/main/kotlin/org/nwapw/abacus/parsing/Tokenizer.kt

@@ -0,0 +1,21 @@
+package org.nwapw.abacus.parsing
+
+/**
+ * Converter from string to tokens.
+ *
+ * Interface that converts a string into a list
+ * of tokens of a certain type.
+ *
+ * @param <T> the type of the tokens produced.
+ */
+interface Tokenizer<out T> {
+
+    /**
+     * Converts a string into tokens.
+     *
+     * @param string the string to convert.
+     * @return the list of tokens, or null on error.
+     */
+    fun tokenizeString(string: String):  List<T>
+
+}

core/src/main/kotlin/org/nwapw/abacus/parsing/TreeBuilder.kt

@@ -0,0 +1,26 @@
+package org.nwapw.abacus.parsing
+
+import org.nwapw.abacus.tree.TreeNode
+
+/**
+ * Class to combine a [Tokenizer] and a [Parser]
+ *
+ * TreeBuilder class used to piece together a Tokenizer and
+ * Parser of the same kind. This is used to essentially avoid
+ * working with any parameters at all, and the generics
+ * in this class are used only to ensure the tokenizer and parser
+ * are of the same type.
+ *
+ * @param <T> the type of tokens created by the tokenizer and used by the parser.
+ */
+class TreeBuilder<T>(private val tokenizer: Tokenizer<T>, private val parser: Parser<T>) {
+
+    /**
+     * Parses the given [string] into a tree.
+     *
+     * @param string the string to parse into a tree.
+     * @return the resulting tree.
+     */
+    fun fromString(string: String): TreeNode = parser.constructTree(tokenizer.tokenizeString(string))
+
+}