diff --git a/whalesong/selfhost/js-assembler/assemble-expression.rkt b/whalesong/selfhost/js-assembler/assemble-expression.rkt
new file mode 100644
index 0000000..bd61c9c
--- /dev/null
+++ b/whalesong/selfhost/js-assembler/assemble-expression.rkt
@@ -0,0 +1,112 @@
+#lang whalesong (require "../selfhost-lang.rkt")
+; #lang typed/racket/base
+
+(require "assemble-structs.rkt"
+         "assemble-helpers.rkt"
+         "assemble-open-coded.rkt"
+         "../compiler/lexical-structs.rkt"
+         "../compiler/il-structs.rkt"
+         racket/string)
+
+(provide assemble-op-expression
+         current-interned-constant-closure-table
+         assemble-current-interned-constant-closure-table)
+
+
+
+
+(: current-interned-constant-closure-table (Parameterof (HashTable Symbol MakeCompiledProcedure)))
+(define current-interned-constant-closure-table
+  (make-parameter ((inst make-hasheq Symbol MakeCompiledProcedure))))
+
+
+(: assemble-current-interned-constant-closure-table (-> String))
+(define (assemble-current-interned-constant-closure-table)
+  (string-join (hash-map
+                  (current-interned-constant-closure-table)
+                  (lambda (a-label a-shell) ; ([a-label : Symbol] [a-shell : MakeCompiledProcedure]) 
+                           (format "var ~a_c=new RT.Closure(~a,~a,void(0),~a);"
+                                   (assemble-label (make-Label (MakeCompiledProcedure-label a-shell)))
+                                   (assemble-label (make-Label (MakeCompiledProcedure-label a-shell)))
+                                   (assemble-arity (MakeCompiledProcedure-arity a-shell))
+                                   (assemble-display-name (MakeCompiledProcedure-display-name a-shell)))))
+                 "\n"))
+
+
+(: assemble-op-expression (PrimitiveOperator Blockht -> String))
+(define (assemble-op-expression op blockht)
+  (cond
+    [(GetCompiledProcedureEntry? op)
+     "M.p.label"]
+    
+    [(MakeCompiledProcedure? op)
+     (cond
+      ;; Small optimization: try to avoid creating the array if we know up front
+      ;; that the closure has no closed values.  It's a constant that we lift up to the toplevel.
+      [(null? (MakeCompiledProcedure-closed-vals op))
+       (define assembled-label (assemble-label (make-Label (MakeCompiledProcedure-label op))))
+       (unless (hash-has-key? (current-interned-constant-closure-table) (MakeCompiledProcedure-label op))
+         (hash-set! (current-interned-constant-closure-table)
+                    (MakeCompiledProcedure-label op)
+                    op))
+       (format "~a_c" assembled-label)]
+      [else
+       (format "new RT.Closure(~a,~a,[~a],~a)"
+               (assemble-label (make-Label (MakeCompiledProcedure-label op)))
+               (assemble-arity (MakeCompiledProcedure-arity op))
+               (string-join (map
+                             assemble-env-reference/closure-capture 
+                             ;; The closure values are in reverse order
+                             ;; to make it easier to push, in bulk, into
+                             ;; the environment (which is also in reversed order)
+                             ;; during install-closure-values.
+                             (reverse (MakeCompiledProcedure-closed-vals op)))
+                            ",")
+               (assemble-display-name (MakeCompiledProcedure-display-name op)))])]
+    
+    [(MakeCompiledProcedureShell? op)
+     (format "new RT.Closure(~a,~a,void(0),~a)"
+             (assemble-label (make-Label (MakeCompiledProcedureShell-label op)))
+             (assemble-arity (MakeCompiledProcedureShell-arity op))
+             (assemble-display-name (MakeCompiledProcedureShell-display-name op)))]
+    
+    [(CaptureEnvironment? op)
+     (format "M.e.slice(0, M.e.length-~a)"
+             (CaptureEnvironment-skip op))]
+    
+    [(CaptureControl? op)
+     (format "M.captureControl(~a,~a)"
+             (CaptureControl-skip op)
+             (let ([tag ; : (U DefaultContinuationPromptTag OpArg)
+                    (CaptureControl-tag op)])
+               (cond [(DefaultContinuationPromptTag? tag)
+                      (assemble-default-continuation-prompt-tag)]
+                     [(OpArg? tag)
+                      (assemble-oparg tag blockht)])))]
+
+    
+    [(MakeBoxedEnvironmentValue? op)
+     (format "[M.e[M.e.length-~a]]"
+             (add1 (MakeBoxedEnvironmentValue-depth op)))]
+
+    [(CallKernelPrimitiveProcedure? op)
+     (open-code-kernel-primitive-procedure op blockht)]
+
+    [(ApplyPrimitiveProcedure? op)
+     (format "M.primitives[~s]._i(M)" (symbol->string (ApplyPrimitiveProcedure-name op)))]
+
+    [(ModuleVariable? op)
+     (format "M.modules[~s].getExports().get(~s)"
+             (symbol->string
+              (ModuleLocator-name
+               (ModuleVariable-module-name op)))
+             (symbol->string (ModuleVariable-name op)))]
+
+    [(PrimitivesReference? op)
+     (format "M.primitives[~s]" (symbol->string (PrimitivesReference-name op)))]
+
+    [(GlobalsReference? op)
+     (format "(M.globals[~s]!==void(0)?M.globals[~s]:M.params.currentNamespace.get(~s))" 
+             (symbol->string (GlobalsReference-name op))
+             (symbol->string (GlobalsReference-name op))
+             (symbol->string (GlobalsReference-name op)))]))