diff --git a/shell/gap-buffer.mu b/shell/gap-buffer.mu
index 893dc176..7abe57c1 100644
--- a/shell/gap-buffer.mu
+++ b/shell/gap-buffer.mu
@@ -24,6 +24,15 @@ fn clear-gap-buffer _self: (addr gap-buffer) {
   clear-grapheme-stack right
 }
 
+fn gap-buffer-capacity _gap: (addr gap-buffer) -> _/ecx: int {
+  var gap/esi: (addr gap-buffer) <- copy _gap
+  var left/eax: (addr grapheme-stack) <- get gap, left
+  var left-data-ah/eax: (addr handle array grapheme) <- get left, data
+  var left-data/eax: (addr array grapheme) <- lookup *left-data-ah
+  var result/eax: int <- length left-data
+  return result
+}
+
 # just for tests
 fn initialize-gap-buffer-with self: (addr gap-buffer), s: (addr array byte) {
   initialize-gap-buffer self, 0x10/capacity
diff --git a/shell/global.mu b/shell/global.mu
index eb70753d..575fd40b 100644
--- a/shell/global.mu
+++ b/shell/global.mu
@@ -1,5 +1,6 @@
 type global {
   name: (handle array byte)
+  input: (handle gap-buffer)
   value: (handle cell)
 }
 
@@ -1851,3 +1852,60 @@ fn apply-height _args-ah: (addr handle cell), out: (addr handle cell), trace: (a
   var result/xmm0: float <- convert height
   new-float out, result
 }
+
+# Accepts an input s-expression, naively checks if it is a definition, and if
+# so saves the gap-buffer to the appropriate global, spinning up a new empty
+# one to replace it with.
+fn maybe-stash-gap-buffer-to-global _globals: (addr global-table), _definition-ah: (addr handle cell), gap: (addr handle gap-buffer) {
+  # if 'definition' is not a pair, return
+  var definition-ah/eax: (addr handle cell) <- copy _definition-ah
+  var _definition/eax: (addr cell) <- lookup *definition-ah
+  var definition/esi: (addr cell) <- copy _definition
+  var definition-type/eax: (addr int) <- get definition, type
+  compare *definition-type, 0/pair
+  {
+    break-if-=
+    return
+  }
+  # if definition->left is neither "def" nor "set", return
+  var left-ah/eax: (addr handle cell) <- get definition, left
+  var _left/eax: (addr cell) <- lookup *left-ah
+  var left/ecx: (addr cell) <- copy _left
+  {
+    var def?/eax: boolean <- symbol-equal? left, "def"
+    compare def?, 0/false
+    break-if-!=
+    var set?/eax: boolean <- symbol-equal? left, "set"
+    compare set?, 0/false
+    break-if-!=
+    return
+  }
+  # locate the global for definition->right->left
+  var right-ah/eax: (addr handle cell) <- get definition, right
+  var right/eax: (addr cell) <- lookup *right-ah
+  var defined-symbol-ah/eax: (addr handle cell) <- get right, left
+  var defined-symbol/eax: (addr cell) <- lookup *defined-symbol-ah
+  var defined-symbol-name-ah/eax: (addr handle stream byte) <- get defined-symbol, text-data
+  var defined-symbol-name/eax: (addr stream byte) <- lookup *defined-symbol-name-ah
+  var index/ecx: int <- find-symbol-in-globals _globals, defined-symbol-name
+  {
+    compare index, -1/not-found
+    break-if-!=
+    return
+  }
+  # stash 'gap' to it
+  var globals/eax: (addr global-table) <- copy _globals
+  var global-data-ah/eax: (addr handle array global) <- get globals, data
+  var global-data/eax: (addr array global) <- lookup *global-data-ah
+  var offset/ebx: (offset global) <- compute-offset global-data, index
+  var dest-global/eax: (addr global) <- index global-data, offset
+  var dest-ah/eax: (addr handle gap-buffer) <- get dest-global, input
+  copy-object gap, dest-ah
+  # initialize a new gap-buffer in 'gap'
+  var dest/eax: (addr gap-buffer) <- lookup *dest-ah
+  var capacity/ecx: int <- gap-buffer-capacity dest
+  var gap2/eax: (addr handle gap-buffer) <- copy gap
+  allocate gap2
+  var gap-addr/eax: (addr gap-buffer) <- lookup *gap2
+  initialize-gap-buffer gap-addr, capacity
+}
diff --git a/shell/sandbox.mu b/shell/sandbox.mu
index 68ea1060..20d9f5fd 100644
--- a/shell/sandbox.mu
+++ b/shell/sandbox.mu
@@ -568,9 +568,7 @@ fn edit-sandbox _self: (addr sandbox), key: byte, globals: (addr global-table),
     # we'll need to revisit where serialization happens.
     store-state data-disk, self, globals
     # run sandbox
-    var data-ah/eax: (addr handle gap-buffer) <- get self, data
-    var _data/eax: (addr gap-buffer) <- lookup *data-ah
-    var data/ecx: (addr gap-buffer) <- copy _data
+    var data-ah/ecx: (addr handle gap-buffer) <- get self, data
     var value-ah/eax: (addr handle stream byte) <- get self, value
     var _value/eax: (addr stream byte) <- lookup *value-ah
     var value/edx: (addr stream byte) <- copy _value
@@ -592,7 +590,7 @@ fn edit-sandbox _self: (addr sandbox), key: byte, globals: (addr global-table),
       break-if-=
       set-cursor-position real-screen, 0/x, 0/y  # for any debug prints during evaluation
     }
-    run data, value, globals, trace, screen-cell, keyboard-cell
+    run data-ah, value, globals, trace, screen-cell, keyboard-cell
     return
   }
   # ctrl-m
@@ -699,10 +697,12 @@ fn edit-sandbox _self: (addr sandbox), key: byte, globals: (addr global-table),
   }
 }
 
-fn run in: (addr gap-buffer), out: (addr stream byte), globals: (addr global-table), trace: (addr trace), screen-cell: (addr handle cell), keyboard-cell: (addr handle cell) {
-  var read-result-storage: (handle cell)
-  var read-result/esi: (addr handle cell) <- address read-result-storage
-  read-cell in, read-result, trace
+fn run _in-ah: (addr handle gap-buffer), out: (addr stream byte), globals: (addr global-table), trace: (addr trace), screen-cell: (addr handle cell), keyboard-cell: (addr handle cell) {
+  var in-ah/eax: (addr handle gap-buffer) <- copy _in-ah
+  var in/eax: (addr gap-buffer) <- lookup *in-ah
+  var read-result-h: (handle cell)
+  var read-result-ah/esi: (addr handle cell) <- address read-result-h
+  read-cell in, read-result-ah, trace
   var error?/eax: boolean <- has-errors? trace
   {
     compare error?, 0/false
@@ -715,7 +715,7 @@ fn run in: (addr gap-buffer), out: (addr stream byte), globals: (addr global-tab
   var eval-result-storage: (handle cell)
   var eval-result/edi: (addr handle cell) <- address eval-result-storage
   debug-print "^", 4/fg, 0/bg
-  evaluate read-result, eval-result, *nil-ah, globals, trace, screen-cell, keyboard-cell, 1/call-number
+  evaluate read-result-ah, eval-result, *nil-ah, globals, trace, screen-cell, keyboard-cell, 1/call-number
   debug-print "$", 4/fg, 0/bg
   var error?/eax: boolean <- has-errors? trace
   {
@@ -723,6 +723,10 @@ fn run in: (addr gap-buffer), out: (addr stream byte), globals: (addr global-tab
     break-if-=
     return
   }
+  # if there was no error and the read-result starts with "set" or "def", save
+  # the gap buffer in the modified global, then create a new one for the next
+  # command.
+  maybe-stash-gap-buffer-to-global globals, read-result-ah, _in-ah
   clear-stream out
   print-cell eval-result, out, trace
   mark-lines-dirty trace