diff --git a/src/runtime/javascript/expr.ts b/src/runtime/javascript/expr.ts
new file mode 100644
index 000000000..fcf3bc0f0
--- /dev/null
+++ b/src/runtime/javascript/expr.ts
@@ -0,0 +1,40 @@
+export class Type {
+  hypos!: Hypo[]
+  name!: string
+  exprs!: Expr[]
+}
+
+export class Hypo {
+  bind_type!: boolean
+  var!: string
+  type!: Type
+}
+
+export class Expr {
+  dummy!: string
+}
+
+export class ExprAbs extends Expr {
+
+}
+export class ExprApp extends Expr {
+
+}
+export class ExprLit extends Expr {
+
+}
+export class ExprMeta extends Expr {
+
+}
+export class ExprFun extends Expr {
+
+}
+export class ExprVar extends Expr {
+
+}
+export class ExprTyped extends Expr {
+
+}
+export class ExprImplArg extends Expr {
+
+}
diff --git a/src/runtime/javascript/ffi.ts b/src/runtime/javascript/ffi.ts
new file mode 100644
index 000000000..015390c8a
--- /dev/null
+++ b/src/runtime/javascript/ffi.ts
@@ -0,0 +1,68 @@
+/* eslint-disable @typescript-eslint/naming-convention */
+
+import ffi from 'ffi-napi'
+import ref, { Pointer } from 'ref-napi'
+import ref_struct from 'ref-struct-di'
+const Struct = ref_struct(ref)
+
+export const PgfExpr = ref.refType(ref.types.void)
+export const PgfLiteral = ref.refType(ref.types.void)
+
+const PgfUnmarshallerVtbl = Struct({
+  eabs: ref.refType(ref.types.void),
+  eapp: ref.refType(ref.types.void),
+  elit: ref.refType(ref.types.void),
+  emeta: ref.refType(ref.types.void),
+  efun: ref.refType(ref.types.void),
+  evar: ref.refType(ref.types.void),
+  etyped: ref.refType(ref.types.void),
+  eimplarg: ref.refType(ref.types.void),
+  lint: ref.refType(ref.types.void),
+  lflt: ref.refType(ref.types.void),
+  lstr: ref.refType(ref.types.void),
+  dtyp: ref.refType(ref.types.void),
+  free_ref: ref.refType(ref.types.void)
+})
+export const PgfUnmarshaller = Struct({
+  vtbl: ref.refType(PgfUnmarshallerVtbl)
+})
+
+const elit = ffi.Callback(PgfExpr, [PgfUnmarshaller, PgfLiteral],
+  function (self, lit: Pointer<any>): any { // eslint-disable-line @typescript-eslint/no-unused-vars
+    console.log('myelit')
+    console.log('  lit', lit)
+    return lit.deref()
+  })
+
+const lint = ffi.Callback(PgfLiteral, [PgfUnmarshaller, ref.types.size_t, ref.refType(ref.types.uint)],
+  function (self, size: number, val: Pointer<number>): any { // eslint-disable-line @typescript-eslint/no-unused-vars
+    console.log('mylint')
+    console.log('  size', size)
+    console.log('  val', val.deref())
+    // const x: number = val.deref()
+    return val
+  })
+
+const free_ref = ffi.Callback(ref.types.void, [PgfUnmarshaller, ref.refType(ref.types.void)],
+  function (self, x: any): void { // eslint-disable-line @typescript-eslint/no-unused-vars
+    console.log('free_ref')
+  })
+
+const vtbl = new PgfUnmarshallerVtbl({
+  eabs: ref.alloc('void').ref(),
+  eapp: ref.alloc('void').ref(),
+  elit: elit as any,
+  emeta: ref.alloc('void').ref(),
+  efun: ref.alloc('void').ref(),
+  evar: ref.alloc('void').ref(),
+  etyped: ref.alloc('void').ref(),
+  eimplarg: ref.alloc('void').ref(),
+  lint: lint as any,
+  lflt: ref.alloc('void').ref(),
+  lstr: ref.alloc('void').ref(),
+  dtyp: ref.alloc('void').ref(),
+  free_ref: free_ref as any
+})
+
+export const unmarshaller = new PgfUnmarshaller({ vtbl: vtbl.ref() })
+export const marshaller = {}
diff --git a/src/runtime/javascript/index.ts b/src/runtime/javascript/index.ts
index a7f192249..8b2079436 100644
--- a/src/runtime/javascript/index.ts
+++ b/src/runtime/javascript/index.ts
@@ -1,6 +1,9 @@
 /* eslint-disable @typescript-eslint/naming-convention */
 
 import errno from './errno'
+import { Expr } from './expr'
+import { unmarshaller, PgfUnmarshaller, PgfExpr, PgfLiteral } from './ffi'
+
 import ffi from 'ffi-napi'
 import ref, { Pointer } from 'ref-napi'
 import ref_struct, { StructObject } from 'ref-struct-di'
@@ -40,13 +43,13 @@ const PgfType = ref.types.void // TODO
 const PgfTypeHypo = ref.types.void // TODO
 const PgfTypeHypoPtr = ref.refType(PgfTypeHypo)
 
-const PgfExpr = ref.types.void // TODO
-const PgfLiteral = ref.types.void // TODO
+// const PgfExpr = ref.types.void // TODO
+// const PgfLiteral = ref.types.void // TODO
 
 const PgfPrintContext = ref.types.void // TODO
 const PgfPrintContextPtr = ref.refType(PgfPrintContext)
 
-const PgfUnmarshaller = ref.types.void // TODO
+// const PgfUnmarshaller = ref.types.void // TODO
 const PgfUnmarshallerPtr = ref.refType(PgfUnmarshaller)
 
 const PgfMarshaller = ref.types.void // TODO
@@ -289,6 +292,14 @@ function newNGF (abstract_name: string, path?: string): PGFGrammar {
   return new PGFGrammar(db, rev)
 }
 
+function readExpr (str: string): Expr {
+  const txt = PgfText_FromString(str)
+  const expr = runtime.pgf_read_expr(txt, unmarshaller.ref())
+  console.log('expr', expr)
+
+  return new Expr()
+}
+
 // ----------------------------------------------------------------------------
 // Exposed library API
 
@@ -297,5 +308,7 @@ export default {
   readPGF,
   bootNGF,
   readNGF,
-  newNGF
+  newNGF,
+
+  readExpr
 }