pit: More VM-style evaluation

4 files changed, 296 insertions, 328 deletions

diff --git a/pit/src/runtime/compile.c b/pit/src/runtime/compile.c
new file mode 100644
index 0000000..a676a61
--- /dev/null
+++ b/pit/src/runtime/compile.c
@@ -0,0 +1,222 @@
+#include <lcq/pit/runtime/compile.h>
+
+#include <stdio.h>
+
+static void call_special_form(pit_runtime *rt, pit_value f, pit_value args) {
+    char buf[256] = {0};
+    switch (pit_value_sort(f)) {
+    case PIT_VALUE_SORT_REF: {
+        pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, f));
+        if (!h) { pit_error(rt, "bad ref for special form"); return; }
+        switch (h->hsort) {
+        case PIT_VALUE_HEAVY_SORT_NATIVEFUNC:
+            h->in.nativefunc.f(rt, args, h->in.nativefunc.data);
+            break;
+        default: {
+            i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
+            buf[end] = 0;
+            pit_error(rt, "attempted to apply non-nativefunc special form: %s", buf);
+            return;
+        }
+        }
+        break;
+    }
+    default: {
+        i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
+        buf[end] = 0;
+        pit_error(rt, "attempted to apply non-function special form: %s", buf);
+        return;
+    }
+    }
+}
+
+static pit_value free_vars(pit_runtime *rt, pit_value initial_bound, pit_value body) {
+    i64 expr_stack_reset = rt->expr_stack->next;
+    pit_value ret = PIT_NIL;
+    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, initial_bound, body)) < 0) {
+        pit_error(rt, "free variable search stack overflow");
+        return PIT_NIL;
+    }
+    while (rt->expr_stack->next > expr_stack_reset) {
+        pit_value boundscur, bound, cur;
+        if (pit_vec_pop(pit_value)(rt->expr_stack, &boundscur) < 0) {
+            pit_error(rt, "free variable search stack underflow");
+            return PIT_NIL;
+        }
+        bound = pit_value_cons_car(rt, boundscur);
+        cur = pit_value_cons_cdr(rt, boundscur);
+        if (pit_value_is_cons(rt, cur)) {
+            pit_value fsym = pit_value_cons_car(rt, cur);
+            bool is_symbol = pit_value_is_symbol(rt, fsym);
+            pit_value fargs = pit_value_cons_cdr(rt, cur);
+            if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "lambda")) {
+                pit_value new_bound = pit_value_list_append(rt, pit_value_cons_car(rt, fargs), bound);
+                fargs = pit_value_cons_cdr(rt, fargs);
+                while (fargs != PIT_NIL) {
+                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, new_bound, pit_value_cons_car(rt, fargs))) < 0) {
+                        pit_error(rt, "free variable search stack overflow");
+                        return PIT_NIL;
+                    }
+                    fargs = pit_value_cons_cdr(rt, fargs);
+                }
+            } else if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "quote")) {
+                /* don't look inside quote!
+                   if we add other special forms, make sure to consider them here if necessary! */
+            } else {
+                while (fargs != PIT_NIL) {
+                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, bound, pit_value_cons_car(rt, fargs))) < 0) {
+                        pit_error(rt, "free variable search stack overflow");
+                        return PIT_NIL;
+                    }
+                    fargs = pit_value_cons_cdr(rt, fargs);
+                }
+                if (!is_symbol) {
+                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, bound, fsym)) < 0) {
+                        pit_error(rt, "free variable search stack overflow");
+                        return PIT_NIL;
+                    }
+                }
+            }
+        } else if (pit_value_is_symbol(rt, cur)) {
+            if (pit_value_list_contains_eq(rt, cur, bound) == PIT_NIL) {
+                ret = pit_value_cons(rt, cur, ret);
+            }
+        }
+    }
+    rt->expr_stack->next = expr_stack_reset;
+    return ret;
+}
+
+static pit_value lambda(pit_runtime *rt, pit_value args, pit_value body) {
+    pit_value expanded = pit_macroexpand(rt, pit_value_cons(rt, pit_symtab_intern_cstr(rt, "progn"), body));
+    fprintf(stderr, "lambda: "); pit_dump_to_file(rt, stderr, expanded, false); fprintf(stderr, "\n");
+    return pit_value_list(rt, 4,
+        pit_symtab_intern_cstr(rt, "lambda"),
+        args,
+        free_vars(rt, args, expanded),
+        pit_compile(rt, expanded)
+    );
+}
+
+static void c_now(pit_runtime *rt, pit_value v) {
+    pit_traversal_push_value(rt, rt->traversal, v);
+}
+
+static void c_eval(pit_runtime *rt, pit_value e) {
+    if (pit_vec_push(pit_value)(rt->expr_stack, e) < 0)
+        pit_error(rt, "evaluation stack overflow");
+}
+
+pit_value pit_compile(pit_runtime *rt, pit_value top) {
+    char buf[256] = {0};
+    pit_value ret = PIT_NIL;
+    i64 expr_stack_reset = rt->expr_stack->next;
+    i64 traversal_reset = rt->traversal->next;
+    fprintf(stderr, "compile: "); pit_dump_to_file(rt, stderr, top, false); fprintf(stderr, "\n");
+    c_eval(rt, top);
+    /* convert the expression tree into "polish notation" in traversal */
+    while (rt->expr_stack->next > expr_stack_reset) {
+        pit_value cur = PIT_NIL;
+        if (rt->error != PIT_NIL) goto end;
+        if (pit_vec_pop(pit_value)(rt->expr_stack, &cur) < 0)
+            pit_error(rt, "evaluation stack underflow");
+        fprintf(stderr, "cur: "); pit_dump_to_file(rt, stderr, cur, false); fprintf(stderr, "\n");
+        if (pit_value_is_cons(rt, cur)) {
+            pit_value fsym = pit_value_cons_car(rt, cur);
+            bool is_symbol = pit_value_is_symbol(rt, fsym);
+            // pit_annotation *ann = pit_annotation_get(rt, pit_value_as_ref(rt, cur));
+            if (is_symbol && pit_symtab_is_symbol_special_form(rt, fsym)) { /* special forms */
+                pit_value f = pit_symtab_fget(rt, fsym);
+                pit_value args = pit_value_cons_cdr(rt, cur);
+                call_special_form(rt, f, args);
+            } else if (is_symbol && pit_symtab_is_symbol_macro(rt, fsym)) { /* macros */
+                i64 end = pit_dump(rt, buf, sizeof(buf) - 1, fsym, true);
+                buf[end] = 0;
+                pit_error(rt, "encountered an unexpanded macro while compiling: %s", buf);
+            } else { /* normal functions */
+                pit_value args = pit_value_cons_cdr(rt, cur);
+                i64 argcount = 0;
+                while (args != PIT_NIL) {
+                    // fprintf(stderr, "push1: "); pit_dump_to_file(rt, stderr, pit_value_cons_car(rt, args), false); fprintf(stderr, "\n");
+                    c_eval(rt, pit_value_cons_car(rt, args));
+                    args = pit_value_cons_cdr(rt, args);
+                    argcount += 1;
+                }
+                if (!is_symbol) {
+                    // fprintf(stderr, "push2: "); pit_dump_to_file(rt, stderr, fsym, false); fprintf(stderr, "\n");
+                    c_eval(rt, fsym);
+                }
+                c_now(rt, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "apply"), pit_value_integer_new(rt, argcount)));
+                if (is_symbol) {
+                    c_now(rt, pit_value_list(rt, 1, pit_symtab_intern_cstr(rt, "fget")));
+                    c_now(rt, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), fsym));
+                }
+            }
+        } else if (pit_value_is_symbol(rt, cur)) { /* unquoted symbols: variable lookup */
+            pit_symtab_entry *ent = pit_symtab_lookup(rt, cur);
+            if (ent->is_keyword) {
+                c_now(rt, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur));
+            } else {
+                c_now(rt, pit_value_list(rt, 1, pit_symtab_intern_cstr(rt, "get")));
+                c_now(rt, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur));
+            }
+        } else { /* other expressions evaluate to themselves! */
+            c_now(rt, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur));
+        }
+    }
+    for (i64 idx = traversal_reset; idx < rt->traversal->next; idx++) {
+        pit_traversal_entry *ent = pit_vec_get(pit_traversal_entry)(rt->traversal, idx);
+        if (ent == NULL) pit_error(rt, "evaluation traversal invalid");
+        if (rt->error != PIT_NIL) goto end;
+        switch (ent->sort) {
+        case PIT_TRAVERSAL_ENTRY_VALUE: {
+            ret = pit_value_cons(rt, ent->in.value, ret);
+            break;
+        }
+        default:
+            pit_error(rt, "unknown traversal entry");
+            ret = PIT_NIL;
+            goto end;
+        }
+    }
+end: {
+        rt->expr_stack->next = expr_stack_reset;
+        rt->traversal->next = traversal_reset;
+        fprintf(stderr, "compiled: "); pit_dump_to_file(rt, stderr, ret, false); fprintf(stderr, "\n");
+        return ret;
+    }
+}
+
+static pit_value impl_sf_quote(pit_runtime *rt, pit_value args, void *data) {
+    (void) data;
+    pit_traversal_push_value(rt, rt->traversal,
+        pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), pit_value_cons_car(rt, args))
+    );
+    return PIT_NIL;
+}
+static pit_value impl_sf_if(pit_runtime *rt, pit_value args, void *data) {
+    (void) data;
+    pit_value c = pit_value_cons_car(rt, args);
+    args = pit_value_cons_cdr(rt, args);
+    pit_value t = pit_value_cons_car(rt, args);
+    args = pit_value_cons_cdr(rt, args);
+    pit_value e = pit_value_cons_car(rt, args);
+    c_now(rt, pit_value_list(rt, 1, pit_symtab_intern_cstr(rt, "if")));
+    c_now(rt, lambda(rt, PIT_NIL, pit_value_list(rt, 1, t)));
+    c_now(rt, lambda(rt, PIT_NIL, pit_value_list(rt, 1, e)));
+    c_eval(rt, c);
+    return PIT_NIL;
+}
+static pit_value impl_sf_lambda(pit_runtime *rt, pit_value args, void *data) {
+    (void) data;
+    pit_value as = pit_value_cons_car(rt, args);
+    pit_value body = pit_value_cons_cdr(rt, args);
+    c_now(rt, lambda(rt, as, body));
+    return PIT_NIL;
+}
+
+void pit_compile_install_special_forms(pit_runtime *rt) {
+    pit_symtab_sfset(rt, pit_symtab_intern_cstr(rt, "quote"), pit_value_nativefunc_new(rt, impl_sf_quote));
+    pit_symtab_sfset(rt, pit_symtab_intern_cstr(rt, "if"), pit_value_nativefunc_new(rt, impl_sf_if));
+    pit_symtab_sfset(rt, pit_symtab_intern_cstr(rt, "lambda"), pit_value_nativefunc_new(rt, impl_sf_lambda));
+}
diff --git a/pit/src/runtime/eval.c b/pit/src/runtime/eval.c
index 1822bc5..3903a64 100644
--- a/pit/src/runtime/eval.c
+++ b/pit/src/runtime/eval.c
@@ -2,127 +2,8 @@
 
 #include <stdio.h>
 
-void pit_vm_call_special_form(pit_runtime *rt, pit_value f, pit_value args) {
-    char buf[256] = {0};
-    switch (pit_value_sort(f)) {
-    case PIT_VALUE_SORT_REF: {
-        pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, f));
-        if (!h) { pit_error(rt, "bad ref for special form"); return; }
-        switch (h->hsort) {
-        case PIT_VALUE_HEAVY_SORT_NATIVEFUNC:
-            h->in.nativefunc.f(rt, args, h->in.nativefunc.data);
-            break;
-        default: {
-            i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-            buf[end] = 0;
-            pit_error(rt, "attempted to apply non-nativefunc special form: %s", buf);
-            return;
-        }
-        }
-        break;
-    }
-    default: {
-        i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-        buf[end] = 0;
-        pit_error(rt, "attempted to apply non-function special form: %s", buf);
-        return;
-    }
-    }
-}
-
-pit_value pit_vm_compile(pit_runtime *rt, pit_value top) {
-    pit_value ret = PIT_NIL;
-    i64 expr_stack_reset = rt->expr_stack->next;
-    i64 traversal_reset = rt->traversal->next;
-    if (pit_vec_push(pit_value)(rt->expr_stack, top) < 0)
-        pit_error(rt, "evaluation stack overflow");
-    /* first, convert the expression tree into "polish notation" in traversal */
-    while (rt->expr_stack->next > expr_stack_reset) {
-        pit_value cur = PIT_NIL;
-        if (rt->error != PIT_NIL) goto end;
-        if (pit_vec_pop(pit_value)(rt->expr_stack, &cur) < 0)
-            pit_error(rt, "evaluation stack underflow");
-        fprintf(stderr, "cur: "); pit_dump_to_file(rt, stderr, cur, false); fprintf(stderr, "\n");
-        if (pit_value_is_cons(rt, cur)) {
-            pit_value fsym = pit_value_cons_car(rt, cur);
-            bool is_symbol = pit_value_is_symbol(rt, fsym);
-            pit_annotation *ann = pit_annotation_get(rt, pit_value_as_ref(rt, cur));
-            if (is_symbol && pit_symtab_is_symbol_special_form(rt, fsym)) { /* special forms */
-                pit_value f = pit_symtab_fget(rt, fsym);
-                pit_value args = pit_value_cons_cdr(rt, cur);
-                pit_vm_call_special_form(rt, f, args);
-            } else if (is_symbol && pit_symtab_is_symbol_macro(rt, fsym)) { /* macros */
-                pit_error(rt, "encountered a macro while evaluating");
-            } else { /* normal functions */
-                pit_value args = pit_value_cons_cdr(rt, cur);
-                i64 argcount = 0;
-                while (args != PIT_NIL) {
-                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons_car(rt, args)) < 0)
-                        pit_error(rt, "evaluation stack overflow");
-                    args = pit_value_cons_cdr(rt, args);
-                    argcount += 1;
-                }
-                if (!is_symbol) {
-                    if (pit_vec_push(pit_value)(rt->expr_stack, fsym) < 0)
-                        pit_error(rt, "evaluation stack overflow");
-                }
-                pit_traversal_push_value(rt, rt->traversal,
-                    pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "apply"), pit_value_integer_new(rt, argcount))
-                );
-                if (is_symbol) {
-                    pit_traversal_push_value(rt, rt->traversal,
-                        pit_value_list(rt, 1, pit_symtab_intern_cstr(rt, "fget"))
-                    );
-                    pit_traversal_push_value(rt, rt->traversal,
-                        pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), fsym)
-                    );
-                }
-            }
-        } else if (pit_value_is_symbol(rt, cur)) { /* unquoted symbols: variable lookup */
-            pit_symtab_entry *ent = pit_symtab_lookup(rt, cur);
-            if (ent->is_keyword) {
-                pit_traversal_push_value(rt, rt->traversal,
-                    pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur)
-                );
-            } else {
-                pit_traversal_push_value(rt, rt->traversal,
-                    pit_value_list(rt, 1, pit_symtab_intern_cstr(rt, "get"))
-                );
-                pit_traversal_push_value(rt, rt->traversal,
-                    pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur)
-                );
-            }
-        } else { /* other expressions evaluate to themselves! */
-            pit_traversal_push_value(rt, rt->traversal,
-                pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "literal"), cur)
-            );
-        }
-    }
-    for (i64 idx = traversal_reset; idx < rt->traversal->next; idx++) {
-        pit_traversal_entry *ent = pit_vec_get(pit_traversal_entry)(rt->traversal, idx);
-        if (ent == NULL) pit_error(rt, "evaluation traversal invalid");
-        if (rt->error != PIT_NIL) goto end;
-        switch (ent->sort) {
-        case PIT_TRAVERSAL_ENTRY_VALUE: {
-            ret = pit_value_cons(rt, ent->in.value, ret);
-            break;
-        }
-        default:
-            pit_error(rt, "unknown traversal entry");
-            ret = PIT_NIL;
-            goto end;
-        }
-    }
-end: {
-        rt->expr_stack->next = expr_stack_reset;
-        rt->traversal->next = traversal_reset;
-        fprintf(stderr, "compiled: "); pit_dump_to_file(rt, stderr, ret, false); fprintf(stderr, "\n");
-        return ret;
-    }
-}
-
 /* add a new stack frame to the vm (with a tag and callsite annotation) */
-void pit_vm_push_code_func(pit_runtime *rt, pit_value code, pit_value tag, pit_annotation ann, pit_value bound) {
+static void vm_push_code_func(pit_runtime *rt, pit_value code, pit_value tag, pit_annotation ann, pit_value bound) {
     pit_callstack_entry ent;
     ent.tag = tag;
     ent.ann = ann;
@@ -135,36 +16,38 @@ void pit_vm_push_code_func(pit_runtime *rt, pit_value code, pit_value tag, pit_a
 }
 
 /* add a new stack frame to the vm (with no annotation) */
-void pit_vm_push_code(pit_runtime *rt, pit_value code) {
+static void vm_push_code(pit_runtime *rt, pit_value code) {
     pit_annotation ann;
     ann.line = -1;
     ann.column = -1;
-    pit_vm_push_code_func(rt, code, PIT_NIL, ann, PIT_NIL);
+    vm_push_code_func(rt, code, PIT_NIL, ann, PIT_NIL);
 }
 
-void pit_vm_push(pit_runtime *rt, pit_value v) {
-    fprintf(stderr, "push: "); pit_dump_to_file(rt, stderr, v, false); fprintf(stderr, "\n");
+static void vm_push(pit_runtime *rt, pit_value v) {
+    // fprintf(stderr, "push: "); pit_dump_to_file(rt, stderr, v, false); fprintf(stderr, "\n");
     if (pit_vec_push(pit_value)(rt->result_stack, v) < 0) {
         pit_error(rt, "vm stack overflow");
     }
 }
 
-pit_value pit_vm_pop(pit_runtime *rt) {
+static pit_value vm_pop(pit_runtime *rt) {
     pit_value ret = PIT_NIL;
     if (pit_vec_pop(pit_value)(rt->result_stack, &ret) < 0) {
         pit_error(rt, "vm stack underflow");
     }
-    fprintf(stderr, "pop: "); pit_dump_to_file(rt, stderr, ret, false); fprintf(stderr, "\n");
+    // fprintf(stderr, "pop: "); pit_dump_to_file(rt, stderr, ret, false); fprintf(stderr, "\n");
     return ret;
 }
 
-void pit_vm_call_lisp(pit_runtime *rt, pit_value tag, pit_value closure, pit_value args) {
+static void vm_call_lisp(pit_runtime *rt, pit_value tag, pit_value closure, pit_value args) {
     pit_value bound = PIT_NIL;
     pit_value env = pit_value_array_get(rt, closure, 0);
     pit_value anames = pit_value_array_get(rt, closure, 1);
     pit_value arg_rest_nm = pit_value_array_get(rt, closure, 2);
     pit_value body = pit_value_array_get(rt, closure, 3);
     if (rt->error != PIT_NIL) return;
+    // fprintf(stderr, "call lisp: "); pit_dump_to_file(rt, stderr, closure, false); fprintf(stderr, "\n");
+    // fprintf(stderr, "binding: "); pit_dump_to_file(rt, stderr, env, false); fprintf(stderr, "\n");
     while (env != PIT_NIL) { /* first, bind all entries in the closure */
         pit_value b = pit_value_cons_car(rt, env);
         pit_value nm = pit_value_cons_car(rt, b);
@@ -190,28 +73,28 @@ void pit_vm_call_lisp(pit_runtime *rt, pit_value tag, pit_value closure, pit_val
     pit_annotation ann;
     ann.line = -1;
     ann.column = -1;
-    pit_vm_push_code_func(rt, body, tag, ann, bound);
+    vm_push_code_func(rt, body, tag, ann, bound);
 }
 
-void pit_vm_call(pit_runtime *rt, pit_value f, pit_value args) {
+static bool vm_call(pit_runtime *rt, pit_value f, pit_value args) {
     char buf[256] = {0};
     if (pit_value_is_symbol(rt, f)) f = pit_symtab_fget(rt, f);
     switch (pit_value_sort(f)) {
     case PIT_VALUE_SORT_REF: {
         pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, f));
-        if (!h) { pit_error(rt, "bad ref for function"); return; }
+        if (!h) { pit_error(rt, "bad ref for function"); return false; }
         switch (h->hsort) {
         case PIT_VALUE_HEAVY_SORT_NATIVEFUNC:
-            pit_vm_push(rt, h->in.nativefunc.f(rt, args, h->in.nativefunc.data));
+            vm_push(rt, h->in.nativefunc.f(rt, args, h->in.nativefunc.data));
             break;
         case PIT_VALUE_HEAVY_SORT_FUNC:
-            pit_vm_call_lisp(rt, h->in.func.nm, h->in.func.closure, args);
+            vm_call_lisp(rt, h->in.func.nm, h->in.func.closure, args);
             break;
         default: {
             i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
             buf[end] = 0;
             pit_error(rt, "attempted to apply non-function ref: %s", buf);
-            return;
+            return false;
         }
         }
         break;
@@ -220,20 +103,21 @@ void pit_vm_call(pit_runtime *rt, pit_value f, pit_value args) {
         i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
         buf[end] = 0;
         pit_error(rt, "attempted to apply non-function value: %s", buf);
-        return;
+        return false;
     }
     }
+    return true;
 }
 
 /* run one instruction of the VM */
 bool pit_vm_run_one(pit_runtime *rt) {
-    char buf[256] = {0};
     if (rt->callstack->next < 1) return false;
     pit_callstack_entry *ent = pit_vec_get(pit_callstack_entry)(rt->callstack, rt->callstack->next - 1);
     if (ent == NULL) {
         pit_error(rt, "malformed call stack");
         return false;
     }
+    // fprintf(stderr, "code: "); pit_dump_to_file(rt, stderr, ent->code, false); fprintf(stderr, "\n");
     pit_value ins = pit_value_cons_car(rt, ent->code);
     if (ins == PIT_NIL) {
         pit_error(rt, "malformed vm instruction");
@@ -246,53 +130,50 @@ bool pit_vm_run_one(pit_runtime *rt) {
         final = true;
         pit_vec_pop(pit_callstack_entry)(rt->callstack, NULL);
     } else ent->code = rest;
-    fprintf(stderr, "ins: "); pit_dump_to_file(rt, stderr, ins, false); fprintf(stderr, "\n");
+    // fprintf(stderr, "ins: "); pit_dump_to_file(rt, stderr, ins, false); fprintf(stderr, "\n");
     pit_value op = pit_value_cons_car(rt, ins);
     if (pit_symtab_symbol_name_match_cstr(rt, op, "literal")) {
-        pit_vm_push(rt, pit_value_cons_car(rt, pit_value_cons_cdr(rt, ins)));
+        /* push a lisp value to the vm stack */
+        vm_push(rt, pit_value_cons_car(rt, pit_value_cons_cdr(rt, ins)));
+    } else if (pit_symtab_symbol_name_match_cstr(rt, op, "lambda")) {
+        /* create and push a function with the given arguments, free variables, and (compiled) body */
+        /* notably, this builds the closure by recording the currently-bound cells for each free variable! */
+        pit_value args = pit_value_cons_cdr(rt, ins);
+        pit_value as = pit_value_cons_car(rt, args);
+        args = pit_value_cons_cdr(rt, args);
+        pit_value freevars = pit_value_cons_car(rt, args); 
+        args = pit_value_cons_cdr(rt, args);
+        pit_value body = pit_value_cons_car(rt, args); 
+        vm_push(rt, pit_value_func_lambda(rt, as, freevars, body));
     } else if (pit_symtab_symbol_name_match_cstr(rt, op, "get")) {
-        pit_vm_push(rt, pit_symtab_get(rt, pit_vm_pop(rt)));
+        pit_value nm = vm_pop(rt);
+        // fprintf(stderr, "get: "); pit_dump_to_file(rt, stderr, nm, false); fprintf(stderr, "\n");
+        vm_push(rt, pit_symtab_get(rt, nm));
+        /* pop a symbol and look up its value */
+        // vm_push(rt, pit_symtab_get(rt, vm_pop(rt)));
     } else if (pit_symtab_symbol_name_match_cstr(rt, op, "fget")) {
-        pit_vm_push(rt, pit_symtab_fget(rt, pit_vm_pop(rt)));
+        /* pop a symbol and look up its function value */
+        vm_push(rt, pit_symtab_fget(rt, vm_pop(rt)));
+    } else if (pit_symtab_symbol_name_match_cstr(rt, op, "if")) {
+        /* pop a then-function, an else-function, and a condition */
+        /* call (no args) the then-function if the condition is true, otherwise call the else-function */
+        pit_value t = vm_pop(rt);
+        pit_value e = vm_pop(rt);
+        pit_value c = vm_pop(rt);
+        if (!vm_call(rt, c != PIT_NIL ? t : e, PIT_NIL)) return false;
     } else if (pit_symtab_symbol_name_match_cstr(rt, op, "apply")) {
+        /* pop an arity n and a function, and then n arguments, and apply the function */
         i64 arity = pit_value_as_integer(rt, pit_value_cons_car(rt, pit_value_cons_cdr(rt, ins)));
-        pit_value f = pit_vm_pop(rt);
+        pit_value f = vm_pop(rt);
         pit_value args = PIT_NIL;
-        while (arity-- > 0) args = pit_value_cons(rt, pit_vm_pop(rt), args);
-        if (pit_value_is_symbol(rt, f)) f = pit_symtab_fget(rt, f);
-        switch (pit_value_sort(f)) {
-        case PIT_VALUE_SORT_REF: {
-            pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, f));
-            if (!h) { pit_error(rt, "bad ref for function"); return PIT_NIL; }
-            switch (h->hsort) {
-            case PIT_VALUE_HEAVY_SORT_NATIVEFUNC:
-                pit_vm_push(rt, h->in.nativefunc.f(rt, args, h->in.nativefunc.data));
-                break;
-            case PIT_VALUE_HEAVY_SORT_FUNC:
-                pit_vm_call_lisp(rt, h->in.func.nm, h->in.func.closure, args);
-                break;
-            default: {
-                i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-                buf[end] = 0;
-                pit_error(rt, "attempted to apply non-function ref: %s", buf);
-                return false;
-            }
-            }
-            break;
-        }
-        default: {
-            i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-            buf[end] = 0;
-            pit_error(rt, "attempted to apply non-function value: %s", buf);
-            return false;
-        }
-        }
+        while (arity-- > 0) args = pit_value_cons(rt, vm_pop(rt), args);
+        if (!vm_call(rt, f, args)) return false;
     } else {
         pit_error(rt, "unknown vm operation");
         return false;
     }
     if (final) { /* if we have finished this stack frame */
-        fprintf(stderr, "unbinding: "); pit_dump_to_file(rt, stderr, bound, false); fprintf(stderr, "\n");
+        // fprintf(stderr, "unbinding: "); pit_dump_to_file(rt, stderr, bound, false); fprintf(stderr, "\n");
         while (bound != PIT_NIL) { /* unbind everything we bound for the frame, in reverse */
             pit_symtab_unbind(rt, pit_value_cons_car(rt, bound));
             bound = pit_value_cons_cdr(rt, bound);
@@ -301,15 +182,18 @@ bool pit_vm_run_one(pit_runtime *rt) {
     return true;
 }
 
-/* run the VM until evaluation finishes, returning the result */
+/* run the VM until evaluation of this code finishes, returning the result */
 pit_value pit_vm_eval(pit_runtime *rt, pit_value v) {
-    pit_vm_push_code(rt, v);
-    while (pit_vm_run_one(rt));
-    pit_vm_pop(rt);
+    i64 start = rt->callstack->next;
+    vm_push_code(rt, v);
+    while (pit_vm_run_one(rt) && rt->callstack->next > start);
+    return vm_pop(rt);
 }
 
+/* run the VM until this function call finishes, returning the result */
 pit_value pit_vm_apply(pit_runtime *rt, pit_value f, pit_value args) {
-    pit_vm_call(rt, f, args);
-    while (pit_vm_run_one(rt));
-    pit_vm_pop(rt);
+    i64 start = rt->callstack->next;
+    vm_call(rt, f, args);
+    while (pit_vm_run_one(rt) && rt->callstack->next > start);
+    return vm_pop(rt);
 }
diff --git a/pit/src/runtime/macroexpand.c b/pit/src/runtime/macroexpand.c
index 7ff1a6a..ffa796d 100644
--- a/pit/src/runtime/macroexpand.c
+++ b/pit/src/runtime/macroexpand.c
@@ -1,6 +1,9 @@
 #include <lcq/pit/runtime/macroexpand.h>
 
+#include <stdio.h>
+
 pit_value pit_macroexpand(pit_runtime *rt, pit_value top) {
+    fprintf(stderr, "macroexpand: "); pit_dump_to_file(rt, stderr, top, false); fprintf(stderr, "\n");
     i64 expr_stack_reset = rt->expr_stack->next;
     i64 result_stack_reset = rt->result_stack->next;
     i64 traversal_reset = rt->traversal->next;
@@ -15,33 +18,14 @@ pit_value pit_macroexpand(pit_runtime *rt, pit_value top) {
             pit_value fsym = pit_value_cons_car(rt, cur);
             bool is_symbol = pit_value_is_symbol(rt, fsym);
             pit_annotation *ann = pit_annotation_get(rt, pit_value_as_ref(rt, cur));
-            if (is_symbol && pit_symtab_is_symbol_macro(rt, fsym)) {
+            if (is_symbol && pit_symtab_is_symbol_special_form(rt, fsym)) {
+                pit_traversal_push_value(rt, rt->traversal, cur);
+            } else if (is_symbol && pit_symtab_is_symbol_macro(rt, fsym)) {
                 pit_value f = pit_symtab_fget(rt, fsym);
                 pit_value args = pit_value_cons_cdr(rt, cur);
-                pit_value res = pit_value_apply(rt, f, args);
+                pit_value res = pit_vm_apply(rt, f, args);
                 if (pit_vec_push(pit_value)(rt->expr_stack, res) < 0)
                     pit_error(rt, "macro expansion stack overflow");
-            } else if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "defer")) {
-                pit_value args = pit_value_cons_cdr(rt, cur);
-                pit_traversal_push_value(rt, rt->traversal, pit_value_cons_car(rt, args));
-            } else if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "quote")) {
-                pit_traversal_push_value(rt, rt->traversal, cur);
-            } else if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "lambda")) {
-                pit_value args = pit_value_cons_cdr(rt, cur);
-                pit_value bindings = pit_value_cons_car(rt, args);
-                pit_value body = pit_value_cons_cdr(rt, args);
-                i64 argcount = 0;
-                if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_list(rt, 2, pit_symtab_intern_cstr(rt, "defer"), bindings)) < 0)
-                    pit_error(rt, "macro expansion stack overflow");
-                while (body != PIT_NIL) {
-                    pit_value a = pit_value_cons_car(rt, body);
-                    if (pit_vec_push(pit_value)(rt->expr_stack, a) < 0)
-                        pit_error(rt, "macro expansion stack overflow");
-                    body = pit_value_cons_cdr(rt, body);
-                    argcount += 1;
-                }
-                pit_traversal_push_application(rt, rt->traversal, argcount + 1, ann);
-                pit_traversal_push_value(rt, rt->traversal, fsym);
             } else {
                 pit_value args = pit_value_cons_cdr(rt, cur);
                 i64 argcount = 0;
@@ -106,6 +90,7 @@ end: {
         rt->expr_stack->next = expr_stack_reset;
         rt->result_stack->next = result_stack_reset;
         rt->traversal->next = traversal_reset;
+        fprintf(stderr, "macroexpand result: "); pit_dump_to_file(rt, stderr, ret, false); fprintf(stderr, "\n");
         return ret;
     }
 }
diff --git a/pit/src/runtime/value/func.c b/pit/src/runtime/value/func.c
index 5f88cb0..ad5ce4c 100644
--- a/pit/src/runtime/value/func.c
+++ b/pit/src/runtime/value/func.c
@@ -1,61 +1,6 @@
 #include <lcq/pit/runtime/value/func.h>
 
-static pit_value free_vars(pit_runtime *rt, pit_value initial_bound, pit_value body) {
-    i64 expr_stack_reset = rt->expr_stack->next;
-    pit_value ret = PIT_NIL;
-    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, initial_bound, body)) < 0) {
-        pit_error(rt, "free variable search stack overflow");
-        return PIT_NIL;
-    }
-    while (rt->expr_stack->next > expr_stack_reset) {
-        pit_value boundscur, bound, cur;
-        if (pit_vec_pop(pit_value)(rt->expr_stack, &boundscur) < 0) {
-            pit_error(rt, "free variable search stack underflow");
-            return PIT_NIL;
-        }
-        bound = pit_value_cons_car(rt, boundscur);
-        cur = pit_value_cons_cdr(rt, boundscur);
-        if (pit_value_is_cons(rt, cur)) {
-            pit_value fsym = pit_value_cons_car(rt, cur);
-            bool is_symbol = pit_value_is_symbol(rt, fsym);
-            pit_value fargs = pit_value_cons_cdr(rt, cur);
-            if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "lambda")) {
-                pit_value new_bound = pit_value_list_append(rt, pit_value_cons_car(rt, fargs), bound);
-                fargs = pit_value_cons_cdr(rt, fargs);
-                while (fargs != PIT_NIL) {
-                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, new_bound, pit_value_cons_car(rt, fargs))) < 0) {
-                        pit_error(rt, "free variable search stack overflow");
-                        return PIT_NIL;
-                    }
-                    fargs = pit_value_cons_cdr(rt, fargs);
-                }
-            } else if (is_symbol && pit_symtab_symbol_name_match_cstr(rt, fsym, "quote")) {
-                /* don't look inside quote!
-                   if we add other special forms, make sure to consider them here if necessary! */
-            } else {
-                while (fargs != PIT_NIL) {
-                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, bound, pit_value_cons_car(rt, fargs))) < 0) {
-                        pit_error(rt, "free variable search stack overflow");
-                        return PIT_NIL;
-                    }
-                    fargs = pit_value_cons_cdr(rt, fargs);
-                }
-                if (!is_symbol) {
-                    if (pit_vec_push(pit_value)(rt->expr_stack, pit_value_cons(rt, bound, fsym)) < 0) {
-                        pit_error(rt, "free variable search stack overflow");
-                        return PIT_NIL;
-                    }
-                }
-            }
-        } else if (pit_value_is_symbol(rt, cur)) {
-            if (pit_value_list_contains_eq(rt, cur, bound) == PIT_NIL) {
-                ret = pit_value_cons(rt, cur, ret);
-            }
-        }
-    }
-    rt->expr_stack->next = expr_stack_reset;
-    return ret;
-}
+#include <stdio.h>
 
 bool pit_value_is_func(pit_runtime *rt, pit_value a) {
     return pit_value_is_ref_heavy_sort(rt, a, PIT_VALUE_HEAVY_SORT_FUNC);
@@ -63,12 +8,13 @@ bool pit_value_is_func(pit_runtime *rt, pit_value a) {
 bool pit_value_is_nativefunc(pit_runtime *rt, pit_value a) {
     return pit_value_is_ref_heavy_sort(rt, a, PIT_VALUE_HEAVY_SORT_NATIVEFUNC);
 }
-pit_value pit_value_func_lambda(pit_runtime *rt, pit_value args, pit_value body) {
+pit_value pit_value_func_lambda(pit_runtime *rt, pit_value args, pit_value freevars, pit_value compiled) {
+    // fprintf(stderr, "lambda args: "); pit_dump_to_file(rt, stderr, args, false); fprintf(stderr, "\n");
+    // fprintf(stderr, "lambda freevars: "); pit_dump_to_file(rt, stderr, freevars, false); fprintf(stderr, "\n");
+    // fprintf(stderr, "lambda compiled: "); pit_dump_to_file(rt, stderr, compiled, false); fprintf(stderr, "\n");
     pit_value ret = pit_value_ref_heavy_new(rt);
     pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, ret));
     if (!h) { pit_error(rt, "failed to create new heavy value for lambda"); return PIT_NIL; }
-    pit_value expanded = pit_macroexpand(rt, pit_value_cons(rt, pit_symtab_intern_cstr(rt, "progn"), body));
-    pit_value freevars = free_vars(rt, args, expanded);
     pit_value env = PIT_NIL;
     while (freevars != PIT_NIL) {
         pit_value sym = pit_value_cons_car(rt, freevars);
@@ -94,7 +40,6 @@ pit_value pit_value_func_lambda(pit_runtime *rt, pit_value args, pit_value body)
         }
     }
     arg_cells = pit_value_list_reverse(rt, arg_cells);
-    pit_value compiled = pit_vm_compile(rt, expanded);
     pit_value closure[4] = {env, arg_cells, arg_rest_nm, compiled};
     h->in.func.nm = PIT_NIL;
     h->in.func.closure = pit_value_array_from_buf(rt, closure, 4);
@@ -112,71 +57,3 @@ pit_value pit_value_nativefunc_new_with_data(pit_runtime *rt, pit_nativefunc f,
 pit_value pit_value_nativefunc_new(pit_runtime *rt, pit_nativefunc f) {
     return pit_value_nativefunc_new_with_data(rt, f, NULL);
 }
-pit_value pit_value_apply(pit_runtime *rt, pit_value f, pit_value args) {
-    char buf[256] = {0};
-    if (pit_value_is_symbol(rt, f)) {
-        f = pit_symtab_fget(rt, f);
-    }
-    /* if f is not a symbol, assume it is a func or nativefunc
-       most commonly, this happens when you funcall a variable
-       with a function in the value cell, e.g. passing a lambda to a function */
-    switch (pit_value_sort(f)) {
-    case PIT_VALUE_SORT_REF: {
-        pit_value_heavy *h = pit_value_ref_deref(rt, pit_value_as_ref(rt, f));
-        if (!h) { pit_error(rt, "bad ref"); return PIT_NIL; }
-        if (h->hsort == PIT_VALUE_HEAVY_SORT_FUNC) {
-            /* calling a Lisp function is simple! */
-            pit_value bound = PIT_NIL;
-            pit_value env = pit_value_array_get(rt, h->in.func.closure, 0);
-            pit_value anames = pit_value_array_get(rt, h->in.func.closure, 1);
-            pit_value arg_rest_nm = pit_value_array_get(rt, h->in.func.closure, 2);
-            pit_value body = pit_value_array_get(rt, h->in.func.closure, 3);
-            if (rt->error != PIT_NIL) return PIT_NIL;
-            while (env != PIT_NIL) { /* first, bind all entries in the closure */
-                pit_value b = pit_value_cons_car(rt, env);
-                pit_value nm = pit_value_cons_car(rt, b);
-                pit_symtab_bind(rt, nm, pit_value_cons_cdr(rt, b));
-                bound = pit_value_cons(rt, nm, bound);
-                env = pit_value_cons_cdr(rt, env);
-            }
-            while (anames != PIT_NIL) { /* bind all argument names to their values */
-                pit_value nm = pit_value_cons_car(rt, anames);
-                pit_value cell = pit_value_cell_new(rt, PIT_NIL);
-                if (arg_rest_nm != PIT_NIL && pit_value_eq(nm, arg_rest_nm)) {
-                    pit_value_cell_set(rt, cell, args, nm);
-                    pit_symtab_bind(rt, nm, cell);
-                    break;
-                } else {
-                    pit_value_cell_set(rt, cell, pit_value_cons_car(rt, args), nm);
-                    pit_symtab_bind(rt, nm, cell);
-                }
-                bound = pit_value_cons(rt, nm, bound);
-                args = pit_value_cons_cdr(rt, args);
-                anames = pit_value_cons_cdr(rt, anames);
-            }
-            /* TODO */ 
-            pit_value ret = body;
-            // pit_value ret = pit_eval(rt, body); /* evaluate the body */
-            while (bound != PIT_NIL) { /* unbind everything we bound earlier, in reverse */
-                pit_symtab_unbind(rt, pit_value_cons_car(rt, bound));
-                bound = pit_value_cons_cdr(rt, bound);
-            }
-            return ret;
-        } else if (h->hsort == PIT_VALUE_HEAVY_SORT_NATIVEFUNC) {
-            /* calling native functions is even simpler */
-            return h->in.nativefunc.f(rt, args, h->in.nativefunc.data);
-        } else {
-            i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-            buf[end] = 0;
-            pit_error(rt, "attempted to apply non-function ref: %s", buf);
-            return PIT_NIL;
-        }
-    }
-    default: {
-        i64 end = pit_dump(rt, buf, sizeof(buf) - 1, f, true);
-        buf[end] = 0;
-        pit_error(rt, "attempted to apply non-function value: %s", buf);
-        return PIT_NIL;
-    }
-    }
-}