A let is a lambda. E.g. (let ((x 1)) body) can be translated into ((lambda (x) body) 1) Furthermore, in Scheme all control and environment structures can be represented by lambda expressions and applications of lambdas. So, lambda is strictly more powerful than let and forms the basis of many of the interesting constructs found … Read more
Just specify explicitly what is the type of pictures: So instead of: let pictures = selectedRestaurant[“Pictures”] as! NSArray Write: let pictures: NSArray = selectedRestaurant[“Pictures”] as! NSArray
def defines a toplevel var, even if you use it in a function or inner loop of some code. What you get in let are not vars. Per the documentation for let: Locals created with let are not variables. Once created their values never change! (Emphasis not mine.) You don’t need mutable state for your … Read more
You could use a temporary list comprehension [(barcode(productId), metric(size)) for name, size in [lookup(productId)]][0] or, equivalently, a generator expression next((barcode(productId), metric(size)) for name, size in [lookup(productId)]) but both of those are pretty horrible. Another (horrible) method is via a temporary lambda, which you call immediately (lambda (name, size): (barcode(productId), metric(size)))(lookup(productId)) I think the recommended “Pythonic” … Read more
When you say let 5 = 10 it’s not a redefinition of 5, it’s a pattern matching, the same which occurs when you say foo 5 = undefined … foo 10 … The pattern simply fails if it’s ever matched. In let-expressions the match is lazy. This means the match is only being done when … Read more
The problem is that your use of let is wrong. let works like this: (let [identifier (expr)]) So your example should be something like this: (let [s (Scanner. “a b c”)] (exprs)) You can only use the lexical bindings made with let within the scope of let (the opening and closing parens). Let just creates … Read more
Basically, use let if the variable’s value will change during the code use const if it won’t and you / your team want to use const in those situations in the project you’re working on; it’s a matter of style If you do use const, then it’s surprising how often it turns out that the … Read more
So, you can use the extension method syntax, which would involve one lambda expression more than you are currently using. There is no let, you just use a multi-line lambda and declare a variable: var results = Stores.Where(store => { var averagePrice = store.Sales.Average(s => s.Price); return averagePrice > 250 && averagePrice < 500; }); … Read more
This is the latest scripture from the Xcode 6.3 Beta / Swift 1.2 release notes: let constants have been generalized to no longer require immediate initialization. The new rule is that a let constant must be initialized before use (like a var), and that it may only be initialized: not reassigned or mutated after initialization. … Read more
Do let statements create properties on the global object? According to the spec, no: A global environment record is logically a single record but it is specified as a composite encapsulating an object environment record and a declarative environment record. The object environment record has as its base object the global object of the associated … Read more