boolean

问题 I have question about SKI-Combinators. Can XOR (exclusive or) be expressed using S and K combinators only? I have True = Cancel False = (Swap Cancel) where Cancel x y = K x y = x Swap: ff x y = S ff x y = ff y x 回答1: Booleans Your question is a bit unclear on the details, but it seems that what you mean is that you have the following representation of booleans: T := K F := S K This works because it means the following reductions hold: T t e => t F t e => e in other words, b t e can be

问题 I'm using Node+Express+Jade to render some webpages. On a form there are 2 checkboxes. When the form is submitted through POST, if the checkbox is checked, I get req.body.checkbox1 -> 'on' , if isn't checked, I get req.body.checkbox1 -> undefined Is possible to get checkbox value as true or false ? Here's my server side test code var bodyParser = require('body-parser'); var express = require('express'); var app = express(); app.use(bodyParser.urlencoded({extended: true})); app.use(express

问题 Is the following piece of code supposed to work? bool b1 = true; bool b2 = 1 < 2; if (b1 == b2) { // do something } I suspect that not all 'trues' are equal. 回答1: Yes. All trues are equal. 回答2: Yes, boolean values can only store true or false, and you can compare the values for equality. However, some bad uses of bool variables can lead to "undefined" behaviours and might look as if it is neither true nor false. For example reading the value of an uninitialized automatic variable or direct

问题 Is the following piece of code supposed to work? bool b1 = true; bool b2 = 1 < 2; if (b1 == b2) { // do something } I suspect that not all 'trues' are equal. 回答1: Yes. All trues are equal. 回答2: Yes, boolean values can only store true or false, and you can compare the values for equality. However, some bad uses of bool variables can lead to "undefined" behaviours and might look as if it is neither true nor false. For example reading the value of an uninitialized automatic variable or direct

问题 I have a dataframe like this: Bool Hour 0 False 12 1 False 24 2 False 12 3 False 24 4 True 12 5 False 24 6 False 12 7 False 24 8 False 12 9 False 24 10 False 12 11 True 24 and I would like to backfill the True value in 'Bool' column to the point when 'Hour' first reaches '12'. The result would be something like this: Bool Hour Result 0 False 12 False 1 False 24 False 2 False 12 True <- desired backfill 3 False 24 True <- desired backfill 4 True 12 True 5 False 24 False 6 False 12 False 7

问题 I have a dataframe like this: Bool Hour 0 False 12 1 False 24 2 False 12 3 False 24 4 True 12 5 False 24 6 False 12 7 False 24 8 False 12 9 False 24 10 False 12 11 True 24 and I would like to backfill the True value in 'Bool' column to the point when 'Hour' first reaches '12'. The result would be something like this: Bool Hour Result 0 False 12 False 1 False 24 False 2 False 12 True <- desired backfill 3 False 24 True <- desired backfill 4 True 12 True 5 False 24 False 6 False 12 False 7

问题 I am working on a project where at a certain moment I need to show for one month which days are still available. There is a function that calculates which days are available. My colleagues said:"Oh we know, you should return a BitVector32. That's the most efficient when working with a list of booleans." I would have used a List<bool> or something like that. A BitVector32 seems to me to be something for low level stuff when you are actually working with bits. So, the question is. Should you

问题 How do I make a query that would return yes/no instead of t/f (true/false)? Current solution is: SELECT credit_card_holders.token IS NOT NULL AS premium I found a Ruby solution: Rails (or Ruby): Yes/No instead of True/False But would rather do it in PostgreSQL if possible. 回答1: Ended up with this: (case when credit_card_holders.token IS NOT NULL then 'Yes' else 'No' end) AS premium 回答2: by creating custom types also you can achieve this, see the following example create table foo (id int,xid

问题 How do I make a query that would return yes/no instead of t/f (true/false)? Current solution is: SELECT credit_card_holders.token IS NOT NULL AS premium I found a Ruby solution: Rails (or Ruby): Yes/No instead of True/False But would rather do it in PostgreSQL if possible. 回答1: Ended up with this: (case when credit_card_holders.token IS NOT NULL then 'Yes' else 'No' end) AS premium 回答2: by creating custom types also you can achieve this, see the following example create table foo (id int,xid

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Is False == 0 and True == 1 in Python an implementation detail or is it guaranteed by the language? I noticed today that the following works using python 2.6 (Cpython)... >>> a=[100,200] >>> a[True] 200 >>> a[False] 100 Is this portable to other python implementations (e.g. is True / False guaranteed to inherit from int? Is True guaranteed to evaluate to 1 instead of some other non-zero number?) Is there any