operator-precedence

问题 I'm building a simple language parser, and having an issue with lower precedence prefix expressions. Here's an example grammar: E = E5 E5 = E4 'OR' E4 | E4 E4 = E3 'AND' E3 | E3 E3 = 'NOT' E3 | E2 E2 = E1 '==' E1 | E1 E1 = '(' E ')' | 'true' | 'false' However, this grammar doesn't work correctly for the NOT , if it's used as the RHS of a higher precedence infix operator, i.e.: true == NOT false This is due to the == operator requiring E1 on the RHS, which cannot be a NOT operation. I'm unsure

问题 I know that inline styles via the 'style' attribute take precedence over those specified in an external css file. But what about stand-alone attributes like 'cellpadding'? An example line would be like this: <table cellpadding="4" class="list"> 回答1: 6.4.4 Precedence of non-CSS presentational hints in the CSS 2.1 spec says: “The UA may choose to honor presentational attributes in an HTML source document. If so, these attributes are translated to the corresponding CSS rules with specificity

问题 I feel like this search query is not working as I imagined it would. I want to be certain that the only items selected are those with ksisoldby identical (though case-insensitive, thus ILIKE ) to $user . And the the other fields specified with the AND s and OR s are possible ways this selection could be narrowed down. "SELECT id, status, customer_id, shipping_address_id, order_number, reference, ship_via_id, order_date :: date, due_date :: date, created, sales_tax, freight, taxable,

问题 There is a feature in Vim I would find so great.. may I ask if it exists or if anyone had an idea about how I would start implementing it? 'Inspired from Mathematica's front end's ctrl-. feature, one would be able to sequentially select, in visual mode, the successive layers of an expression the cursor is taken into. For, example, if we consider the following expression in an imaginary langage: # enter visual mode at this position: for(i in 1:n){ a = append(a, b[i %% floor((n + 1) / 2)] + c -

问题 This question already has answers here : Why are these constructs using pre and post-increment undefined behavior? (14 answers) Closed 6 years ago . Please have a look at following code snippet: int a = 10, b; b = (a) + (++a); //2 printf("b = %d\n", b); Output: b = 22 In statement 2, there are 4 distinct operators. Out of which () has highest precedence. Since associativity of () operator is left to right why b = 22 and not 21 ? $ gcc --version gcc (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3 回答1: b

问题 Why is it that: Function definitions can use definitions defined after it while variable definitions can't. For example, a) the following code snippet is wrong: ; Must define function `f` before variable `a`. #lang racket (define a (f)) (define (f) 10) b) While the following snippet is right: ; Function `g` could be defined after function `f`. #lang racket (define (f) (g)) ; `g` is not defined yet (define (g) 10) c) Right too : ; Variable `a` could be defined after function `f` #lang racket

问题 this is a program problem from leetcode.it gives an unsigned int n，ask you to return the numbers of bit '1'; int hammingWeight(uint32_t n) { int num=0; for(;n!=0;n=n>>1) { if(n&1==1) { num++; } } return num; } this works perfectly,but int hammingWeight(uint32_t n) { int num=0; for(;n!=0;n=n>>1) { if(1==n&1) { num++; } } return num; } this one cant work sometimes! i guess something is wrong when 1 calculate with an uint32_t,but i cant understand this clearly. 回答1: == has higher precedence than

问题 In OCaml, when using a let to assign an alias to a short-circuit operator ( && or || ), it no longer short-circuits evaluation of the operands. This is not intuitive. What is the reason for this behavior? Consider the following code: let f() = Printf.printf "f"; false;; let g() = Printf.printf "g"; true;; let a = (&&);; f() && g();; (* outputs 'f' *) (&&) (f()) (g());; (* outputs 'f' *) a (f()) (g());; (* outputs 'gf' *) This also happens with let ... in , so let b = (&&) in b (f()) (g());;

问题 Note: this is a more detailed version of Recursive Descent precedence parsing missing prefix expression I'm building a simple language parser, and having an issue with lower precedence prefix expressions. Here's an example grammar: E = E8 E8 = E7 'OR' E8 | E7 E7 = E6 'XOR' E7 | E6 E6 = E5 'AND' E6 | E5 E5 = 'NOT' E5 | E4 E4 = E3 '==' E4 | E3 '!=' E4 | E3 E3 = E2 '<' E3 | E2 '>' E3 | E2 E2 = E1 '+' E2 | E1 '-' E2 | E1 '*' E2 | E1 '+' E2 | E1 E1 = '(' E ')' | 'true' | 'false' | '0'..'9' However

问题 I apply a simple anonymous function to return c(x,x+5) on the sequence 1:5 I expect to see c(1,6,2,7,3,8,4,9,5,10) (the concatenation of the subresults) but instead the result vector is unwantedly sorted. What is doing that and how do I prevent it? > (function(x) c(x,x+5)) (1:5) [1] 1 2 3 4 5 6 7 8 9 10 However applying the function on each individual argument is right: > (function(x) c(x,x+5)) (1) [1] 1 6 > (function(x) c(x,x+5)) (2) [1] 2 7 ... > (function(x) c(x,x+5)) (5) [1] 5 10 回答1: You