add if statement and declaration

src/runtime/declaration/declaration.c

@@ -0,0 +1,18 @@
+#include "declaration.h"
+
+ArErr runtime_declaration(Translated *translated, RuntimeState *state,
+                          struct Stack *stack) {
+  int64_t length = pop_bytecode(translated, state);
+  int64_t offset = pop_bytecode(translated, state);
+  int64_t prehash = pop_bytecode(translated, state);
+  int64_t from_register = pop_byte(translated, state);
+  int64_t source_location_index = pop_bytecode(translated, state);
+  uint64_t hash = runtime_hash(arena_get(&translated->constants, offset), length, prehash);
+  ArgonObject * exists = hashmap_lookup_GC(stack->scope, hash);
+  if (exists) {
+    SourceLocation *source_location = darray_get(&translated->source_locations, source_location_index);
+    return create_err(source_location->line, source_location->column, source_location->length, state->path, "Runtime Error", "Identifier '%.*s' has already been declared in the current scope", length, arena_get(&translated->constants, offset));
+  }
+  hashmap_insert_GC(stack->scope, hash, arena_get(&translated->constants, offset), state->registers[from_register], 0);
+  return no_err;
+}