pattern-matching

I'm coding in SML for an assignment and I've done a few practice problems and I feel like I'm missing something- I feel like I'm using too many case statements. Here's what I'm doing and the problem statements for what I'm having trouble with.: Write a function all_except_option, which takes a string and a string list. Return NONE if the string is not in the list, else return SOME lst where lst is like the argument list except the string is not in it. fun all_except_option(str : string, lst : string list) = case lst of [] => NONE | x::xs => case same_string(x, str) of true => SOME xs | false =

I had a List of Scala tuples like the following: val l = List((1,2),(2,3),(3,4)) and I wanted to map it in a list of Int where each item is the sum of the Ints in a the corresponding tuple. I also didn't want to use to use the x._1 notation so I solved the problem with a pattern matching like this def addTuple(t: (Int, Int)) : Int = t match { case (first, second) => first + second } var r = l map addTuple Doing that I obtained the list r: List[Int] = List(3, 5, 7) as expected. At this point, almost by accident, I discovered that I can achieve the same result with an abbreviated form like the

So I'm trying to find square brackets inside a string: s = "testing [something] something else" x,y = string.find(s,"[") which gives me an error: malformed pattern (missing ']'). I also tried: x,y = string.find(s,"\[") giving me the same error. And this: x,y = string.find(s,"\\[") in this case x and y are nil. Any thoughts on how to do this properly? Thanks in advance. John's answer will work -- turning off pattern matching. What you're trying to do -- escape the [ -- is done with the % character in Lua: x,y = string.find(s,'%[') Also strings in Lua all have the string module as their

I would like to do some multiline matching with bash's =~ #!/bin/bash str='foo = 1 2 3 bar = what about 42? boo = more words ' re='bar = (.*)' if [[ "$str" =~ $re ]]; then echo "${BASH_REMATCH[1]}" else echo no match fi Almost there, but if I use ^ or $ , it will not match, and if I don't use them, . eats newlines too. EDIT: sorry, values after = could be multi-word values. I could be wrong, but after a quick read from here , especially Note 2 at the end of the page, bash can sometimes include the newline character when matching with the dot operator. Therefore, a quick solution would be: #!

Apart from: case class A ... case which is quite useful? Why do we need to use case in match ? Wouldn't: x match { y if y > 0 => y * 2 _ => -1 } ... be much prettier and concise? Or why do we need to use case when a function takes a tuple? Say, we have: val z = List((1, -1), (2, -2), (3, -3)).zipWithIndex Now, isn't: z map { case ((a, b), i) => a + b + i } ... way uglier than just: z map (((a, b), i) => a + b + i) ...? The second issue, anonymous functions that avoid the case , is a matter of debate: https://groups.google.com/d/msg/scala-debate/Q0CTZNOekWk/z1eg3dTkCXoJ Also: http://www.scala

I recently inquired about why PatternTest was causing a multitude of needless evaluations: PatternTest not optimized? Leonid replied that it is necessary for what seems to me as a rather questionable method. I can accept that, though I would prefer a more efficient alternative. I now realize, which I believe Leonid has been saying for some time, that this problem runs much deeper in Mathematica , and I am troubled. I cannot understand why this is not or cannot be better optimized. Consider this example: list = RandomReal[9, 20000]; Head /@ list; // Timing MatchQ[list, {x__Integer, y__}] //