Added alternate expression parser.

This adds an alternate expression parser designed solely for arithmetic
operations.

1 files changed, 101 insertions, 0 deletions

diff --git a/dice-lang/src/bjc/dicelang/expr/Tokens.java b/dice-lang/src/bjc/dicelang/expr/Tokens.java
new file mode 100644
index 0000000..08e7197
--- /dev/null
+++ b/dice-lang/src/bjc/dicelang/expr/Tokens.java
@@ -0,0 +1,101 @@
+package bjc.dicelang.expr;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Contains per-instance state for token parsing.
+ *
+ * @author EVE
+ *
+ */
+public class Tokens {
+	/*
+	 * Contains mappings from variable references to string names.
+	 */
+	private final Map<Integer, String> symTab;
+	/*
+	 * Reverse index into the symbol table.
+	 */
+	private final Map<String, Integer> revSymTab;
+
+	/**
+	 * Read-only view on the symbol table.
+	 */
+	public final Map<Integer, String> symbolTable;
+
+	/*
+	 * Next index into the symbol table
+	 */
+	private int nextSym;
+
+	/*
+	 * Mapping from literal tokens to token types.
+	 */
+	private final Map<String, TokenType> litTokens;
+
+	/**
+	 * Create a new set of tokens.
+	 */
+	public Tokens() {
+		symTab = new HashMap<>();
+		revSymTab = new HashMap<>();
+
+		symbolTable = Collections.unmodifiableMap(symTab);
+
+		nextSym = 0;
+
+		litTokens = new HashMap<>();
+
+		litTokens.put("+", TokenType.ADD);
+		litTokens.put("-", TokenType.SUBTRACT);
+		litTokens.put("*", TokenType.MULTIPLY);
+		litTokens.put("/", TokenType.DIVIDE);
+		litTokens.put("(", TokenType.OPAREN);
+		litTokens.put(")", TokenType.CPAREN);
+	}
+
+	/**
+	 * Convert the string representation of a token into a token.
+	 *
+	 * @param tok
+	 *                The string repr. of the token.
+	 * @param raw
+	 *                The original string the token came from.
+	 *
+	 * @return The token the string represents.
+	 */
+	public Token lexToken(String tok, String raw) {
+		if(litTokens.containsKey(tok))
+			return new Token(litTokens.get(tok), raw, this);
+		else
+			return parseVRef(tok, raw);
+	}
+
+	/*
+	 * Parse a variable reference.
+	 */
+	private Token parseVRef(String tok, String raw) {
+		Token tk = new Token(TokenType.VREF, raw, this);
+
+		if(revSymTab.containsKey(tok)) {
+			/*
+			 * Reuse the entry if it exists.
+			 */
+			tk.intValue = revSymTab.get(tok);
+		} else {
+			/*
+			 * Create a new entry.
+			 */
+			tk.intValue = nextSym;
+
+			symTab.put(nextSym, tok);
+			revSymTab.put(tok, nextSym);
+
+			nextSym += 1;
+		}
+
+		return tk;
+	}
+}