1 files changed, 73 insertions, 0 deletions
diff --git a/eval.c b/eval.c
new file mode 100644
index 0000000..5841566
--- /dev/null
+++ b/eval.c
@@ -0,0 +1,73 @@
+#include <assert.h>
+#include <stdio.h>
+
+#include "eval.h"
+
+static int evaluate_value(const struct Node* node, long* out)
+{
+    switch (node->kind)
+    {
+        case VALUE_DIFFERENCE:
+            *out = (long)node->first->character - (long)node->second->character;
+            return 0;
+        default: break;
+    }
+
+    assert(!"the parser handed a non-value where a value goes");
+    return 1;
+}
+
+static int evaluate_type(const struct Node* node, struct Type* out)
+{
+    out->kind = KIND_VOID;
+    out->number = 0;
+    switch (node->kind)
+    {
+        case TYPE_DECLTYPE:
+            if (evaluate_value(node->first, &out->number))
+                return 1;
+            out->kind = KIND_VALUE;
+            return 0;
+        default: break;
+    }
+
+    assert(!"the parser handed a non-type where a type goes");
+    return 1;
+}
+
+static enum RunStatus emit(const struct Node* node)
+{
+    struct Type type;
+    if (evaluate_type(node->first, &type))
+        return RUN_FAILED;
+
+    if (type.kind == KIND_VALUE)
+        (void)printf("%ld\n", type.number);
+    return RUN_DONE;
+}
+
+static enum RunStatus execute_one(const struct Node* node)
+{
+    switch (node->kind)
+    {
+        case STMT_EMIT: return emit(node);
+        default: break;
+    }
+
+    assert(!"the parser handed a non-statement where a statement goes");
+    return RUN_FAILED;
+}
+
+enum RunStatus execute(const struct Node* statement)
+{
+    while (statement != NULL)
+    {
+        enum RunStatus status = execute_one(statement);
+        if (status != RUN_DONE)
+            return status;
+
+        statement = statement->next;
+    }
+
+    return RUN_DONE;
+}