.

Makefile

@@ -35,7 +35,8 @@ DEBUG_CFLAGS=-Og -ggdb3 ${WARNINGS} -fno-omit-frame-pointer -fsanitize=address -
   -DCHECK_TYCHE_BUGS=1
 DEBUG_LDFLAGS=-fsanitize=address -fsanitize=undefined
 
-UNAME_S := $(shell uname -s)   # apple clang doesn't support -fsanitize=leak
+# apple clang doesn't support -fsanitize=leak
+UNAME_S := $(shell uname -s)
 ifneq ($(UNAME_S),Darwin)
   DEBUG_CFLAGS += -fsanitize=leak
   DEBUG_LDFLAGS += -fsanitize=leak

lib/stack.c

@@ -55,6 +55,7 @@ static TYC_RESULT stack_peek(Stack* s, VALUE* v_out)
 {
     if (s->stack_n < stack_top_fp(s))
         return T_ERR_STACK_UNDERFLOW;
+    if (v_out)
         *v_out = s->stack[s->stack_n - 1];
     return T_OK;
 }
@@ -73,9 +74,17 @@ static size_t stack_len(Stack* s)
     return s->stack_n - stack_top_fp(s);
 }
 
-static VALUE stack_get(Stack* s, int32_t key)
+static TYC_RESULT stack_at(Stack* s, int32_t key, VALUE* v)
 {
-    abort(); // TODO
+    if (key >= 0) {
+        *v = s->stack[stack_top_fp(s) + key];
+    } else {
+        if (stack_top_fp(s) + s->stack_n + key < 0)
+            return T_ERR_STACK_ACCESS_OUT_OF_RANGE;
+        *v = s->stack[s->stack_n + key];
+    }
+
+    return T_OK;
 }
 
 static void stack_set(Stack* s, int32_t key, VALUE v)

lib/tyche.h

@@ -7,7 +7,7 @@ typedef enum {
 
 typedef enum {
     T_OK = 0,
-    T_ERR_STACK_UNDERFLOW = -1, T_ERR_STACK_FP_UNDERFLOW = -2,
+    T_ERR_STACK_UNDERFLOW = -1, T_ERR_STACK_FP_UNDERFLOW = -2, T_ERR_STACK_ACCESS_OUT_OF_RANGE = -3,
 } TYC_RESULT;
 
 #endif //TYCHE_TYCHE_H

test/tests.c

@@ -10,21 +10,41 @@
 int main()
 {
     // values
+    {
         printf("### Values\n");
         assert(value_type(create_value_integer(42)) == TT_INTEGER);
         assert(value_integer(create_value_integer(-42)) == -42);
         assert(fabsf(value_real(create_value_real(42.4f)) - 42.4f) < 0.00001f);
         assert(value_idx(create_value_idx(TT_FUNCTION, 42)) == 42);
+    }
 
-    // values
+    // stack
+    {
         printf("### Stack\n");
+
         Stack s;
         stack_init(&s);
+
         stack_push(&s, create_value_integer(10));
         stack_push(&s, create_value_integer(20));
         stack_push(&s, create_value_integer(30));
 
+        VALUE v;
         assert(stack_len(&s) == 3);
+        assert(stack_at(&s, 0, &v) == T_OK); assert(value_integer(v) == 10);
+        assert(stack_at(&s, 1, &v) == T_OK); assert(value_integer(v) == 20);
+        assert(stack_at(&s, -1, &v) == T_OK); assert(value_integer(v) == 30);
+        assert(stack_at(&s, -2, &v) == T_OK); assert(value_integer(v) == 20);
+
+        assert(stack_pop(&s, NULL) == T_OK);
+        assert(stack_pop(&s, NULL) == T_OK);
+        assert(stack_at(&s, -1, &v) == T_OK); assert(value_integer(v) == 10);
+        assert(stack_pop(&s, NULL) == T_OK);
+        assert(stack_len(&s) == 0);
+
+        assert(stack_pop(&s, NULL) == T_ERR_STACK_UNDERFLOW);
 
         stack_finalize(&s);
     }
+
+}