diff --git a/stages/lisp0/lisp.asm b/stages/lisp0/lisp.asm
index b8a0b72..d3f0302 100644
--- a/stages/lisp0/lisp.asm
+++ b/stages/lisp0/lisp.asm
@@ -117,30 +117,40 @@ extern dealloc
     PLUS_STR db "+"
     PLUS_STR_LEN equ $ - PLUS_STR
 
-    ;; add $rdi and $rsi
+    ;; sum list $rdi in env $rsi
 p_add:
+    sub rsp, 24
+    call eval_list
+    mov qword [rsp], rax        ; evaled list
+    mov qword [rsp + 8], rsi    ; env
+    mov qword [rsp + 16], 0        ; acc = 0
+.add_loop:
+    mov rdi, qword [rsp]        ; $rdi = evaled list
+    call get_cdr
+    mov qword [rsp], rax            ; update list to cdr
+    call get_car
+    mov rdi, rax                    ; $rdi = car
     call obj_tag_part
     cmp al, OBJ_NUM
     jne .invalid
     call obj_addr_part
-    mov rdx, qword [rax + 8]    ; num1
-    mov rdi, rsi
-    call obj_tag_part
-    cmp al, OBJ_NUM
-    jne .invalid
-    call obj_addr_part
-    mov rax, qword [rax + 8]    ; num2
-    add rax, rdx                ; num1 + num2
-    push rax
-    mov rdi, 16                 ; struct { refcount: usize, value: i64 }
+    mov rax, qword [rax + 8]        ; num
+    add qword [rsp + 16], rax        ; acc += num
+    mov rdi, qword [rsp]            ; $rdi = list
+    lea rsi, [rel nil]
+    cmp rdi, rsi
+    jne .add_loop
+.done:
+    mov rdi, 16
     mov rsi, 8
     call alloc
-    mov [rax], 1           ; refcount = 1
-    pop rdx
-    mov qword [rax + 8], rdx     ; value = sum
     mov rdi, rax
+    mov dword [rdi], 1          ; refcount = 1
+    mov rax, qword [rsp + 16]        ; acc
+    mov qword [rdi + 8], rax     ; value = acc
     mov rsi, OBJ_NUM
     call obj_set_tag
+    add rsp, 24
     ret
 .invalid:
     xor rdi, rdi
@@ -863,6 +873,8 @@ apply:
 .apply_prim:
     call obj_addr_part
     mov rax, qword [rax + 8]    ; get the function pointer
+    mov rdi, rsi                ; $rdi = argument list
+    mov rsi, rdx                ; $rsi = environment
     jmp rax
 .invalid_func:
     xor rdi, rdi