Compute FIRST sets correctly

spec/compiler/build_tables/next_symbols_spec.cpp

@@ -0,0 +1,38 @@
+#include "spec_helper.h"
+#include "build_tables/next_symbols.h"
+#include "grammar.h"
+#include "rules.h"
+
+using std::set;
+using namespace build_tables;
+using namespace rules;
+
+START_TEST
+
+describe("computing FIRST sets", []() {
+    Grammar grammar({
+        { "A", choice({
+            seq({
+                sym("B"),
+                sym("x"),
+                sym("B") }),
+            sym("B") }) },
+        { "B", choice({
+            seq({
+                sym("y"),
+                sym("z"),
+                sym("y") }),
+            sym("y") }) },
+    });
+    
+    describe("for a rule", [&]() {
+        it("searches the tree for terminals", [&]() {
+            auto terminals = next_terminals(grammar.rules.find("A")->second, grammar);
+            AssertThat(terminals, Equals(set<Symbol>({
+                Symbol("y")
+            })));
+        });
+    });
+});
+
+END_TEST