diff --git a/include/data.s b/include/data.s
index 4a827e2..35c4c8d 100644
--- a/include/data.s
+++ b/include/data.s
@@ -1,7 +1,7 @@
 
 .ifndef _data_s_file
 _data_s_file:
-	nop
+	nop # avoid confusing gdb
 
 # Format of the info tables:
 # - code
@@ -64,6 +64,62 @@ IND_info:
 IND_code:
 	enter 010(%rbp)
 
+# Blackhole (contains the original thunkptr for debugging purposes)
+# | ptr | orig_thunkptr |
+BLE_evacuate:
+	jmp _gc_evacuate_ret
+BLE_scavenge:
+	jmp _gc_scavenge_ret
+
+BLE_info_table:
+	cell BLE_evacuate
+	cell BLE_scavenge
+	cell 0
+BLE_code:
+	# if we hit this, we've got a pure loop in a program, and it is never
+	# going to actually progress. So let's just shoot it down with a
+	# helpful message or so.
+	mov 010(%rbp), %r15
+
+	mov $1, %rdi #stdout
+
+	mov $14, %rdx
+	mov $BLE_msg, %rsi
+	mov $1, %rax #write
+	syscall
+
+	mov $1, %rdx
+	BLE_loop:
+	mov %r15, %rcx
+	and $0xf, %rcx
+	mov $BLE_hex, %rsi
+	add %rcx, %rsi
+	mov $1, %rax
+	syscall
+	shr $4, %r15
+	jnz BLE_loop
+
+	mov $BLE_nl, %rsi
+	mov $1, %rax
+	syscall
+
+	# shot self down (and retry if it doesn't succeed)
+	BLE_retry_sigkill:
+	mov $39, %rax
+	syscall # getpid
+	mov %rax, %rdi
+	mov $6, %rsi # SIGABRT
+	mov $62, %rax # kill
+	syscall
+	jmp BLE_retry_sigkill
+
+BLE_msg:
+	.ascii "diverged at 0x"
+BLE_hex:
+	.ascii "0123456789abcdef"
+BLE_nl:
+	.ascii "\n"
+
 # List
 # | ptr | 0 |           # [] case
 # | ptr | 1 | a | b |   # (a:b) case
@@ -86,7 +142,7 @@ LIST_scavenge:
 	cmpq $0, 010(%rbp)
 	je LIST_scavenge_nil
 	mov %rbp, %r15
-	
+
 	mov $LIST_scavenge1, %rsi
 	mov 020(%r15), %rbp
 	jmp _gc_evacuate
diff --git a/include/gc.s b/include/gc.s
index ae71d5c..b40ac95 100644
--- a/include/gc.s
+++ b/include/gc.s
@@ -96,7 +96,7 @@ _uskel_alloc:
 
 _uskel_gc_init:
 	mov %rsi, %r13
-	movq $0x100, _gc_min_alloc # must be higher than 2x the biggest thunk possible
+	movq $0x100000, _gc_min_alloc # must be higher than 2x the biggest thunk possible
 	movq $0x180, _gc_grow_ratio
 	movq $0x40, _gc_shrink_ratio
 	mov $0, %rsp # fake original rsp for first alloc run
@@ -124,7 +124,7 @@ _uskel_gc:
 	# point the writer to the new memory area
 	mov _write_region_end, %rsp
 	mov %rsp, %r8 # % r8 is the "last thing that was scavenged"
-	
+
 	# start by evacuating the thunk and cont
 	mov _gc_backup_thunk, %rbp
 	mov $_uskel_gc_evacuate_cont_thunk, %rsi
@@ -167,7 +167,7 @@ _uskel_gc:
 	mov _gc_region_start, %rdi # addr = gc start
 	sub %rdi, %rsi # len = gc end - gc start
 	syscall
-	
+
 	# recalculate the gc trigger point
 	mov %rsp, %rax
 	sub _write_region_start, %rax
diff --git a/include/intops.s b/include/intops.s
index dbadb37..08b3300 100644
--- a/include/intops.s
+++ b/include/intops.s
@@ -5,13 +5,13 @@ _intops_s_file:
 .include "include/primops.s"
 
 .primop2 plus
-	mov 010(%rsi), %rax # arg 2 
+	mov 010(%rsi), %rax # arg 2
 	mov 020(%rbp), %rsi # location of arg1
 	add 010(%rsi), %rax # arg 1
 	primop2_ret_int %rax
 
 .primop2 mul
-	mov 010(%rsi), %rax # arg 2 
+	mov 010(%rsi), %rax # arg 2
 	mov 020(%rbp), %rsi # location of arg1
 	mulq 010(%rsi) # arg 1 (goes to %rax and %rdx)
 	primop2_ret_int %rax
@@ -19,7 +19,7 @@ _intops_s_file:
 .primop2 sub
 	mov 020(%rbp), %rdi # location of arg1
 	mov 010(%rdx), %rax # arg 1
-	sub 010(%rsi), %rax # arg 2 
+	sub 010(%rsi), %rax # arg 2
 	primop2_ret_int %rax
 
 .endif # _intops_s_file
diff --git a/include/io.s b/include/io.s
index 0431dd0..29a63c9 100644
--- a/include/io.s
+++ b/include/io.s
@@ -10,6 +10,7 @@ _io_s_file:
 
 # arg -> | ret | cont |
 .thunkcode print_fini
+	needs_alloc $0110 #64 bit characters + 8 backup
 	mov 010(%rsi), %rax
 
 	# make a string
@@ -25,7 +26,7 @@ _io_s_file:
 	shr $1, %rax
 	jnz print_fini_loop
 
-	mov $0, %rdi #stdin
+	mov $1, %rdi #stdout
 	mov %rsp, %rdx
 	sub %r15, %rdx #size
 	mov %r15, %rsi #buf
diff --git a/include/uskel.s b/include/uskel.s
index f59a1f7..0a21217 100644
--- a/include/uskel.s
+++ b/include/uskel.s
@@ -32,10 +32,10 @@ _uskel_start:
 	pushq $0
 	pushq $main
 
-	mov $0, %rsi # set continuation to exit
+	# loop the continuation to itself (prevents gc trouble, should never be reached)
+	mov %rsp, %rsi
 	enter %rsp # run the program
 	# Q: are there gonna be functions that have both the argument AND the cont?
-	# 
 	# A: No, stuff is either entered as return-continuation (takes res,
 	# cont has to be saved) or as forward call (takes cont)
 	#
diff --git a/sumac.s b/sumac.s
new file mode 100644
index 0000000..d53382c
--- /dev/null
+++ b/sumac.s
@@ -0,0 +1,40 @@
+
+
+.include "include/uskel.s"
+
+.include "include/data.s"
+.include "include/io.s"
+.include "include/intops.s"
+
+.primop2 sumac
+	needs_alloc $0100
+
+	mov 020(%rbp), %rdi #1st arg
+	mov 010(%rdi), %rcx #1st arg val
+	mov 010(%rsi), %rax #2nd arg val
+
+	cmp $0, %rcx
+	jz sumac_ret
+
+	add %rcx, %rax
+	dec %rcx
+	thunkto %r10, $INT_code, %rcx
+	thunkto %r11, $INT_code, %rax
+	thunkto %r10, $sumac, $2, %r10, %r11
+	primop2_cont_indirect %r10
+
+	sumac_ret:
+	primop2_ret_int %rax
+
+.thunkcode main
+	needs_alloc $0150
+
+	thunkto %r11, $INT_code, $10000000
+	thunkto %r12, $INT_code, $0
+	thunkto %r11, $sumac, $2, %r11, %r12
+
+	thunkto %r11, $print, $1, %r11
+	thunkto %rsi, $main_exit, $0
+	enter %r11
+
+.include "include/main_exit.s"
diff --git a/zipfib.s b/zipfib.s
new file mode 100644
index 0000000..493a2ae
--- /dev/null
+++ b/zipfib.s
@@ -0,0 +1,67 @@
+
+.include "include/uskel.s"
+
+.include "include/listops.s"
+.include "include/intops.s"
+.include "include/io.s"
+.include "include/main_exit.s"
+.include "include/apply.s"
+
+# TODO this seems to fill the memory with plus_fini thunks; find out why.
+
+.thunkcode zipWith
+	needs_alloc $070
+	thunkto %rsi, $zipWith_arg1, $5, 020(%rbp), 030(%rbp), 040(%rbp), %rbp, %rsi
+	enter 030(%rbp)
+
+.thunkcode zipWith_arg1
+	movq $zipWith_fini, (%rbp)
+	mov %rsi, 030(%rbp)
+	mov %rbp, %rsi
+	mov 040(%rbp), %rbp
+	enter_rbp
+
+.thunkcode zipWith_fini
+	needs_alloc $0150
+	mov 030(%rbp), %r8 # arg1
+	mov %rsi, %r9 # arg2
+	cmpq $0, 010(%r8)
+	je zipWith_null
+	cmpq $0, 010(%r9)
+	je zipWith_null
+
+	# f (head arg1) (head arg2) : zipWith f (tail arg1) (tail arg2)
+	thunkto %r10, $zipWith, $3, 020(%rbp), 030(%r8), 030(%r9)
+	thunkto %r11, $apply, $3, 020(%rbp), 020(%r8), 020(%r9)
+	thunkto %rsi, $LIST_code, $1, %r11, %r10
+
+	zipWith_ret:
+	mov 050(%rbp), %r8
+	movq $IND_code, 000(%r8)
+	mov %rsi, 010(%r8)
+	mov 060(%rbp), %rbp
+	enter_rbp
+
+	zipWith_null:
+	thunkto %rsi, $LIST_code, $0
+	jmp zipWith_ret
+
+
+.thunkcode main
+	needs_alloc $0370
+	# x = 0 : 1 : zipWith plus x (tail x)
+	thunkto %r8, $FUN2_code, $plus, $0
+	thunkto %r8, $zipWith, $3, %r8, $0, $0
+	thunkto %r9, $INT_code, $1
+	thunkto %r9, $LIST_code, $1, %r9, %r8
+	thunkto %r10, $INT_code, $0
+	thunkto %r10, $LIST_code, $1, %r10, %r9
+	# recurse args!
+	mov %r10, 030(%r8)
+	mov %r9, 040(%r8)
+
+	thunkto %r8, $INT_code, $20
+	thunkto %r8, $list_int_index, $2, %r8, %r10
+	thunkto %r8, $print, $1, %r8
+	thunkto %rsi, $main_exit, $0
+	enter %r8