guard-clause

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 let bindings are unlike C# const variables? just use capital letters and [<Literal>] them and it works as

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 example is solving quadratic functions: type Solution = | NoRoot | OneRoot of float | TwoRoots of float *

I have this simple F# function: let compareNum x = let y = 10 match x with | _ when x = y -> 0 | _ when x > y -> 1 | _ when x < y -> -1 However, F# compiler gives me "Incomplete pattern matches on this expression" warning. In this case, all cases should cover every pattern. I also see a similar example in "Pattern Matching" section in the 1st edition of Programming F# book by Chris Smith. So something might be changed in the later version of F#? Tomas Petricek I think the answer to the previous question (and the comments -- "In general, it is an anti-pattern to have a when guard in the last

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 of guard clauses on the public methods. I am aware of the .NET 4.0 Code Contracts however this is not an