On Oct 28, 2009, at 9:20 PM, Adam wrote:
Reading the older docs for [let and [let* I see that the [let* form
evaluates the bindings sequentially rather than in parallel.
What order are the :> bindings evaluated?
I'm just curious as I haven't used the :> form yet.
As Jon said, :> binds the value (or values) currently on the top of
the stack at the point in the code where the :> appears. So you could
get the former effect of [let ] (that is, binding all the variables in
parallel) by calculating all the values and then binding the variables
all at once like so:
1 2 +
3 4 *
5 6 - :> ( x y z )
In this case, the "1 2 +", "3 4 *", and "5 6 -" expressions all get
evaluated first, and their results are bound to "x", "y", and "z"
afterward at the site of the :>. This would be equivalent to the old
[let ] form:
[let |
x [ 1 2 + ]
y [ 3 4 * ]
z [ 5 6 - ]
| ]
To get the effect of [let* ], you bind each variable immediately after
its value is evaluated:
1 2 + :> x
3 4 * :> y
5 6 - :> z
Thus, "1 2 +" is evaluated and the result bound to "x", then "3 4 *"
is evaluated and the result bound to "y", and finally "5 6 -" is
evaluated and the result bound to "z".
I hope that clarifies it for you, Adam. Let me know if it's still
unclear.
-Joe
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