diff options
Diffstat (limited to 'fsharp.html.markdown')
| -rw-r--r-- | fsharp.html.markdown | 22 |
1 files changed, 13 insertions, 9 deletions
diff --git a/fsharp.html.markdown b/fsharp.html.markdown index 809a1da2..bbf477ba 100644 --- a/fsharp.html.markdown +++ b/fsharp.html.markdown @@ -175,7 +175,12 @@ module ListExamples = // list comprehensions (aka generators) let squares = [for i in 1..10 do yield i * i] - // prime number generator + // A prime number generator + // - this is using a short notation for the pattern matching syntax + // - (p::xs) is 'first :: tail' of the list, could also be written as p :: xs + // this means this matches 'p' (the first item in the list), and xs is the rest of the list + // this is called the 'cons pattern' + // - uses 'rec' keyword, which is necessary when using recursion let rec sieve = function | (p::xs) -> p :: sieve [ for x in xs do if x % p > 0 then yield x ] | [] -> [] @@ -346,7 +351,7 @@ module DataTypeExamples = let trySendEmail email = match email with // use pattern matching | ValidEmailAddress address -> () // send - | InvalidEmailAddress address -> () // dont send + | InvalidEmailAddress address -> () // don't send // The combination of union types and record types together // provide a great foundation for domain driven design. @@ -403,11 +408,14 @@ module ActivePatternExamples = // "banana clips" are the syntax for active patterns + // You can use "elif" instead of "else if" in conditional expressions. + // They are equivalent in F# + // for example, define an "active" pattern to match character types... let (|Digit|Letter|Whitespace|Other|) ch = if System.Char.IsDigit(ch) then Digit - else if System.Char.IsLetter(ch) then Letter - else if System.Char.IsWhiteSpace(ch) then Whitespace + elif System.Char.IsLetter(ch) then Letter + elif System.Char.IsWhiteSpace(ch) then Whitespace else Other // ... and then use it to make parsing logic much clearer @@ -426,7 +434,7 @@ module ActivePatternExamples = // ----------------------------------- // You can create partial matching patterns as well - // Just use underscore in the defintion, and return Some if matched. + // Just use underscore in the definition, and return Some if matched. let (|MultOf3|_|) i = if i % 3 = 0 then Some MultOf3 else None let (|MultOf5|_|) i = if i % 5 = 0 then Some MultOf5 else None @@ -627,7 +635,3 @@ module NetCompatibilityExamples = For more demonstrations of F#, go to the [Try F#](http://www.tryfsharp.org/Learn) site, or my [why use F#](http://fsharpforfunandprofit.com/why-use-fsharp/) series. Read more about F# at [fsharp.org](http://fsharp.org/). - - - - |