diff --git a/Makefile b/Makefile
index 431fcac..386499d 100644
--- a/Makefile
+++ b/Makefile
@@ -87,7 +87,7 @@ lib/compiler.o: lib/compiler.c lib/compiler/compiler.lua.h
 # executable files
 #
 
-LIB_SRC=lib/value.o lib/stack.o lib/array.o lib/table.o lib/heap.o lib/vm.o lib/compiler.o lib/code.o lib/utils.o
+LIB_SRC=lib/value.o lib/stack.o lib/array.o lib/table.o lib/heap.o lib/vm.o lib/step.o lib/compiler.o lib/code.o lib/utils.o
 
 tyche: CFLAGS += ${RELEASE_CFLAGS}
 tyche: LDFLAGS += ${RELEASE_LDFLAGS}
diff --git a/lib/priv.h b/lib/priv.h
index 4398ce1..36f9af9 100644
--- a/lib/priv.h
+++ b/lib/priv.h
@@ -225,4 +225,10 @@ const char*    code_const_string(Code const* code, size_t n);
 uint32_t       code_n_functions(Code const* code);
 Instruction    code_next_instruction(Code const* code, uint32_t function_id, uint32_t pc);
 
+//
+// VM
+//
+
+TYC_RESULT step(TycheVM* T);
+
 #endif //TYCHE_PRIV_H
diff --git a/lib/step.c b/lib/step.c
new file mode 100644
index 0000000..26249c3
--- /dev/null
+++ b/lib/step.c
@@ -0,0 +1,10 @@
+#include "priv.h"
+
+#include <stdlib.h>
+
+TYC_RESULT step(TycheVM* T)
+{
+    abort();
+    return T_OK;
+}
+
diff --git a/lib/vm.c b/lib/vm.c
index 4b0dd76..ab1fd46 100644
--- a/lib/vm.c
+++ b/lib/vm.c
@@ -2,39 +2,138 @@
 
 #include <stdlib.h>
 
+typedef struct Location {
+    uint32_t function_id;
+    uint32_t pc;
+} Location;
+
+typedef struct LocationStack {
+    Location* locations;
+    size_t    sz;
+    size_t    cap;
+} LocationStack;
+
 struct TycheVM {
-    Stack* stack;
-    Heap*  heap;
-    Code*  code;
+    Stack*        stack;
+    Heap*         heap;
+    Code*         code;
+    LocationStack location_stack;
 };
 
+//
+// CREATE/DESTROY VM
+//
+
 TycheVM* tyc_new(void)
 {
     TycheVM* t = xcalloc(1, sizeof(TycheVM));
     t->stack = stack_new();
     t->heap = heap_new();
     t->code = code_new();
+    t->location_stack = (LocationStack) {
+        .locations = xmalloc(4 * sizeof(Location)),
+        .cap = 4,
+        .sz = 0,
+    };
     return t;
 }
 
 void tyc_destroy(TycheVM* t)
 {
+    free(t->location_stack.locations);
     code_destroy(t->code);
     heap_destroy(t->heap);
     stack_destroy(t->stack);
     free(t);
 }
 
+//
+// LOCATION STACK
+//
+
+static void push_location(TycheVM* T, uint32_t function_id, uint32_t pc)
+{
+    if (T->location_stack.sz == T->location_stack.cap) {
+        T->location_stack.cap *= 2;
+        T->location_stack.locations = xrealloc(T->location_stack.locations, T->location_stack.cap * sizeof(Location));
+    }
+
+    T->location_stack.locations[T->location_stack.sz] = (Location) {
+        .function_id = function_id,
+        .pc = pc,
+    };
+    ++T->location_stack.sz;
+}
+
+//
+// CODE LOADING AND EXECUTION
+//
+
 TYC_RESULT tyc_load_bytecode(TycheVM* T, uint8_t const* bytecode, size_t bytecode_sz)
 {
-    return code_load_bytecode(T->code, bytecode, bytecode_sz);
+    TYC_RESULT r;
+    if ((r = code_load_bytecode(T->code, bytecode, bytecode_sz)) != T_OK)
+        return r;
+    if ((r = stack_push(T->stack, create_value_idx(TT_FUNCTION, 0 /* main */))) != T_OK)
+        return r;
+    return T_OK;
+}
+
+static TYC_RESULT enter_function(TycheVM* T, uint16_t n_pars)
+{
+    TYC_RESULT r;
+
+    // get parameters
+    VALUE params[n_pars + 1];
+    for (uint16_t i = 0; i < n_pars; ++i)
+        if ((r = stack_pop(T->stack, &params[i])) != T_OK)
+            return r;
+
+    // get function
+    VALUE function;
+    if ((r = stack_pop(T->stack, &function)) != T_OK)
+        return r;
+    if (value_type(function) != TT_FUNCTION)
+        return T_ERR_TYPE_UNEXPECTED;
+
+    // enter function
+    push_location(T, value_idx(function), 0);
+    stack_push_fp(T->stack);
+
+    // pass parameters
+    for (int i = n_pars-1; i >= 0; --i)
+        if ((r = stack_push(T->stack, params[i])) != T_OK)
+            return r;
+
+    return T_OK;
+}
+
+static TYC_RESULT run_until_return(TycheVM* T)
+{
+    TYC_RESULT r;
+
+    size_t level = stack_fp_level(T->stack);
+    while (stack_fp_level(T->stack) >= level)
+        if ((r = step(T)) != T_OK)
+            return r;
+
+    return T_OK;
 }
 
 TYC_RESULT tyc_call(TycheVM* T, uint16_t n_pars)
 {
-    abort();  // TODO
+    TYC_RESULT r;
+    if ((r = enter_function(T, n_pars)) != T_OK)
+        return r;
+    if ((r = run_until_return(T)) != T_OK)
+        return r;
+    return T_OK;
 }
 
+//
+// STACK MANIPULATION AND QUERY
+//
+
 size_t tyc_stack_size(TycheVM* T)
 {
     return stack_len(T->stack);