Homework 4

src/cd/frontend/semantic/SymTable.java

@@ -0,0 +1,76 @@
+package cd.frontend.semantic;
+
+import cd.frontend.semantic.SemanticFailure.Cause;
+import cd.ir.Symbol;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+
+/** 
+ * A simple symbol table, with a pointer to the enclosing scope. 
+ * Used by {@link TypeChecker} to store the various scopes for
+ * local, parameter, and field lookup. */
+public class SymTable<S extends Symbol> {
+	
+	private final Map<String, S> map = new HashMap<String, S>();
+	
+	private final SymTable<S> parent;
+	
+	public SymTable(SymTable<S> parent) {
+		this.parent = parent;
+	}
+	
+	public void add(S sym) {
+		// check that the symbol is not already declared *at this level*
+		if (containsLocally(sym.name))
+			throw new SemanticFailure(Cause.DOUBLE_DECLARATION);
+		map.put(sym.name, sym);
+	}
+
+	public Collection<S> localSymbols() {
+		return this.map.values();
+	}
+	
+	/**
+	 * True if there is a declaration with the given name at any
+	 * level in the symbol table
+	 */
+	public boolean contains(String name) {
+		return get(name) != null;
+	}
+
+	/** 
+	 * True if there is a declaration at THIS level in the symbol
+	 * table; may return {@code false} even if a declaration exists
+	 * in some enclosing scope
+	 */
+	public boolean containsLocally(String name) {
+		return this.map.containsKey(name);
+	}
+
+	/** 
+	 * Base method: returns {@code null} if no symbol by that
+	 * name can be found, in this table or in its parents */
+	public S get(String name) {
+		S res = map.get(name);
+		if (res != null)
+			return res;
+		if (parent == null)
+			return null;
+		return parent.get(name);
+	}
+	
+	/**
+	 * Finds the symbol with the given name, or fails with a 
+	 * NO_SUCH_TYPE error.  Only really makes sense to use this
+	 * if S == TypeSymbol, but we don't strictly forbid it... */
+	public S getType(String name) {
+		S res = get(name);
+		if (res == null)
+			throw new SemanticFailure(
+					Cause.NO_SUCH_TYPE,
+					"No type '%s' was found", name);
+		return res;
+	}
+}