The following snippet:

open System
open Microsoft.FSharp
open Microsoft.FSharp.Quotations

let t = Var.Global("t",(typeof<float * float>))
let a = Var.Global("a",(typeof<float>))
let b = Var.Global("b",(typeof<float>))
let v = Expr.NewTuple [Expr.Value 0.; Expr.Value 1.]
let e = Expr.Let( t, v
, Expr.Let( a, Expr.TupleGet(Expr.Var t,0)
, Expr.Let(b, Expr.TupleGet(Expr.Var t,1)
,Expr.Var a )))

fails in FSI with:

Microsoft.FSharp.Core.FailureException: error when building 'tupleGet': tuple access out of range.
at Microsoft.FSharp.Core.Operators.failwith[T](String message)
at Microsoft.FSharp.Text.PrintfImpl.go@487@487[B,C,D](String fmt@487, Int32 len@487, FastFunc`2 outputChar@487, FastFunc`2 outa@487, B os@487, FastFunc`2 finalize@487, List`1 args, Int32 i)
at <StartupCode$FSharp.Core>.$Reflect.clo@545.Invoke(A inp)
at Microsoft.FSharp.Quotations.Patterns.mkTupleGet(Type ty, Int32 n, Expr x)

The quotation generated by:

<@@
let t = (0., 1.)
let (a,b) = t
a
@@>

is

Let (t, NewTuple (Value (0.0), Value (1.0)),
Let (patternInput@225, t,
Let (b, TupleGet (patternInput@225, 1),
Let (a, TupleGet (patternInput@225, 0), a))))

which looks identical (apart from the extra level of indirection created by patternInput@225).

Any ideas what I'm doing wrong?

(I'm using F# 1.9.6.0 with .NET 3.5)

Rgds,

Mat