guard-clause

问题 I came across with the following code recently and it bothers me a lot lowerSafeForeignCall dflags block | (entry, middle, CmmForeignCall { .. }) <- blockSplit block = do -- do block stuffs -- Block doesn't end in a safe foreign call: | otherwise = return block This piece of code is from https://phabricator.haskell.org/rGHCb0534f78a73f972e279eed4447a5687bd6a8308e in file compiler/cmm/CmmLayoutStack.hs line 983 I really would like to konw what is this <- in the second line. I believe

问题 I came across with the following code recently and it bothers me a lot lowerSafeForeignCall dflags block | (entry, middle, CmmForeignCall { .. }) <- blockSplit block = do -- do block stuffs -- Block doesn't end in a safe foreign call: | otherwise = return block This piece of code is from https://phabricator.haskell.org/rGHCb0534f78a73f972e279eed4447a5687bd6a8308e in file compiler/cmm/CmmLayoutStack.hs line 983 I really would like to konw what is this <- in the second line. I believe

来源： https://stackoverflow.com/questions/49814220/does-pattern-match-in-raku-have-guard-clause

来源： https://stackoverflow.com/questions/49814220/does-pattern-match-in-raku-have-guard-clause

问题 Is it possible in F# to pattern match directly against a let binding? For example, this compiles without any warnings: let value = match arg with | 1 -> "value1" | 2 -> "value2" | _ -> failwith "key not found" Whereas the following gives the warning "This rule will never be matched" against the lines matching key2 and _ : let key1 = 1 let key2 = 2 let value = match arg with | key1 -> "value1" | key2 -> "value2" | _ -> failwith "key not found" Is this because although they're immutable, the

问题 I define a point type TimeSeriesPoint<'T> = { Time : DateTimeOffset Value : 'T } and a series type TimeSeries<'T> = TimeSeriesPoint<'T> list where I assume the points in this list are ordered by time. I am trying to zip two time series, where, in general, they will have points with the same time, but there might be some points missing in either of them. Any idea why I get a warning for incomplete pattern matches in the code below? let zip (series1 : TimeSeries<float>) (series2 : TimeSeries

问题 In ML-family languages, people tend to prefer pattern matching to if/else construct. In F#, using guards within pattern matching could easily replace if/else in many cases. For example, a simple delete1 function could be rewritten without using if/else (see delete2 ): let rec delete1 (a, xs) = match xs with | [] -> [] | x::xs' -> if x = a then xs' else x::delete1(a, xs') let rec delete2 (a, xs) = match xs with | [] -> [] | x::xs' when x = a -> xs' | x::xs' -> x::delete2(a, xs') Another

问题 What approaches do people take (if any) in managing guard clause explosion in your classes? For example: public void SomeMethod<T>(string var1, IEnumerable<T> items, int count) { if (string.IsNullOrEmpty(var1)) { throw new ArgumentNullException("var1"); } if (items == null) { throw new ArgumentNullException("items"); } if (count < 1) { throw new ArgumentOutOfRangeException("count"); } ... etc .... } In the project that I am currently working on there are many classes that have a similar set

问题 What approaches do people take (if any) in managing guard clause explosion in your classes? For example: public void SomeMethod<T>(string var1, IEnumerable<T> items, int count) { if (string.IsNullOrEmpty(var1)) { throw new ArgumentNullException("var1"); } if (items == null) { throw new ArgumentNullException("items"); } if (count < 1) { throw new ArgumentOutOfRangeException("count"); } ... etc .... } In the project that I am currently working on there are many classes that have a similar set

问题 A common surprise for beginning F# programmers is the fact that the following is an incomplete match: let x, y = 5, 10 match something with | _ when x < y -> "Less than" | _ when x = y -> "Equal" | _ when x > y -> "Greater than" But I just encountered a situation that surprised me. Here's a small bit of sample code to demonstrate it: type Tree = | Leaf of int | Branch of Tree list let sapling = Branch [Leaf 1] // Small tree with one leaf let twoLeafTree = Branch [Leaf 1; Leaf 2] let describe