[Haskell-cafe] trace output statements

[erik]

Tom,

Why does "b" evaluate before "a" in your example? I would have thought
left-hand and then right-hand if needed. I'm on my phone but I'd like to
try the same example with booleans and `&&` instead of `+`.

Erik


On Sat, Dec 22, 2018, 11:40 PM Tom Ellis <
tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk wrote:

> On Sat, Dec 22, 2018 at 09:52:18AM +0100, Damien Mattei wrote:
> > i have inserted trace statement that output variable
> > ... i have strange behavior of output:
>
> Let's take a simpler example.  Do you understand why the trace statments
> from this small program appear in the order that they do?  (And for what
> it's worth I really think you'll be better off writing programs using do
> notation).
>
>
> % cat test.hs
> import Debug.Trace
>
> result =
>   let a = trace "evaluating a" 2
>       b = trace "evaluating b" 10
>       c = trace "evaluating c" (a + b)
>   in c
> ~% ghci -e result test.hs
> evaluating c
> evaluating b
> evaluating a
> 12
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