Back to Questions
925
views2
comments
Translating if-then to match syntax, with inequality condition
f#

Assume b, c, d, x, y are defined.

Consider the following code:

let a =
if b < c then x
else y

I have translated it into "match" syntax as follows, which seems slightly artificial because I am not exactly matching b with the conditions, due to the inequality

let a =
match b with
| _ when ( b < c ) -> x
| _ -> y

and sure enough, I noticed that the following also compiles, replacing "b" with "d" in the match statement:

let a =

match d with

| _ when ( b < c ) -> x

| _ -> y

which is really lame because "d" is not even used in evaluating the conditions.

Is there some more natural way to express the initial code snippet, since I believe if-then is not really considered native in F# ?

.

You should use if-then-else.

The fact that "6.6.3 of the spec

[link:research.microsoft.com]

says that if-then-else has equivalent semantics to a pattern match" ought not be construed as a reason to not use if-then-else.

By on 3/20/2009 2:41 PM ()

I'm not sure why it's "really lame" -- you didn't want to use the value, so you didn't use it...

Anyways, I'd write it like this, if I had to use a match.

let a = match (b < c) with true -> x | _ -> y

But if/then/else works fine and is arguably more clear.

By on 3/20/2009 2:41 PM ()

    Topic tags

    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper