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Sometimes expressions has two states. the result of analyses might be two different things but at the end, there might be the same answer(result) for them.(the way we get to the answer is different,but the result is the same)

for example:

P->Q = M

P->T = M

in lambda we have two solutions.

1.sending with name. (in ALGOL it have over load)

2.sending with value


Q: (λy.(yy) (λx.(xx)a))

1.sending with name

(λx.(xx)a λx.(xx)a)


2.sending with value

(λy.(yy) aa)


now here is the question, in sending with name that used λ (counting), how does the process happen? How this sending (transmittal) happen? How does it work?

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migrated from Nov 28 '11 at 20:38

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I don't understand the question. – Qiaochu Yuan Nov 28 '11 at 23:14
This question would have been perfect for the upcoming Computer Science Stack Exchange. So, if you like to have a place for questions like this one, please go ahead and help this proposal to take off! – Raphael Dec 8 '11 at 21:42

These I know as call-by-name and call-by-value. For a more extensive description see this article on lambda calculus, or this more general article.

In call by value, we evaluate the argument first, so given

(λy.(yy) (λx.(xx)a))

we evaluate (λx.(xx)a) = aa to get (λy.(yy) (aa)) and thence to ((aa)(aa)).

In call by name, we delay the evaluation of (λx.(xx)a) and get


by replacing y in the first function with (λx.(xx)a), then finally we evaluate each of the remaining functions to get ((aa)(aa))

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In ICT, the first strategy is called eager evaluation (evaluate as soon as you can) and the second lazy evaluation (evaluate only if you have to). – Sjoerd Nov 29 '11 at 1:54

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