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Subject: Re: [boost] [yap] review part 3: tests + misc + summary
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2018-02-21 17:31:18
AMDG
On 02/21/2018 10:11 AM, Zach Laine via Boost wrote:
> On Wed, Feb 21, 2018 at 10:28 AM, Steven Watanabe via Boost <
> boost_at_[hidden]> wrote:
>
>> On 02/20/2018 11:16 PM, Zach Laine via Boost wrote:
>>> On Tue, Feb 20, 2018 at 9:29 AM, Steven Watanabe via Boost <
>>> boost_at_[hidden]> wrote:
>>> <snip>
>>> That looks like a great candidate for an example, so I made one out of
>> it:
>>>
>>> https://github.com/tzlaine/yap/commit/4b383f9343a2a8affaf132c5be1eeb
>> 99a56e58df
>>>
>>> <snip>
>>> [snip]
>>>
>>
>> evaluate(let(_a = 1_p << 3) [
>> _a << "1", _a << "2"
>> ], std::cout); // prints 3132, but should print 312
>>
>
> Why should that print out 312? Isn't equivalent to:
>
> std::cout << 3 << "1", std::cout << 3 << "2"
>
> ? If not, why not?
>
The expected behavior is that _a is
a local variable, not macro-like substitution.
let(_a=<expr>) [ <body> ]
should be equivalent to
auto _a = <expr>;
{
<body>;
}
rather than:
#define _a <expr>
<body>;
>
>> Also,
>> let(_a=_a+_a)[let(_a=_a+_a)[let(_a=_a+_a)[...]]]
>> has exponential cost.
>
>
> Sure. It's also not allowed, though. From the let docs:
>
Right. Assume the whole thing is wrapped in let(_a=1_p)[]
and then it is legal. (each _a refers to the _a in the
outer scope.)
In Christ,
Steven Watanabe
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