Comments on: F#: Convert sequence to comma separated string

By: Jonathan Graehl

Jonathan Graehl — Sat, 01 Aug 2009 05:22:13 +0000

let reduceDefault f z s =
    if Seq.isEmpty s then z
    else Seq.reduce f s
let ConvertToCommaSeparatedString s = reduceDefault (fun x y -> x+","+y) "" s

roger, nice trick - but it's wrong if your sequence starts with at least one empty string.

By: _St

_St — Fri, 31 Jul 2009 08:42:41 +0000

Hello, I believe that String.Join Method could the job, too.

By: Carlo

Carlo — Fri, 10 Jul 2009 08:47:31 +0000

Dolphin Smalltalk does it like this which I thought was quite clever. I know this is not a functional style.

do: operation separatedBy: separator
"Evaluate the argument, operation, for each of the
receiver's elements, interspersed with evaluations of the
argument, separator. The separator is first evaluated after the first
element, and is not evaluated after the last element (i.e. it is not evaluated
at all if there are less than two elements)."

| sep |
sep := [sep := separator]. "Switch to the real separator after first eval."
self do:
[:each |
sep value.
operation value: each]

Squeak and most other Smalltalks do something like the following:

do: elementBlock separatedBy: separatorBlock
"Evaluate the elementBlock for all elements in the receiver,
and evaluate the separatorBlock between."

| beforeFirst |
beforeFirst := true.
self do:
[:each |
beforeFirst
ifTrue: [beforeFirst := false]
ifFalse: [separatorBlock value].
elementBlock value: each]

By: roger

roger — Thu, 09 Jul 2009 13:52:44 +0000

I like your last solution, but you could also check if the current state of acc and conditionally add the comma 'in front' with the 2nd entry. fun acc x -> (if acc "" then "," else "") + x...if's are expressions.