pattern-matching

Is it possible, with simple F# pattern matching transformations, to ignore unmatched values without a warning?

So, I previously asked this question: http://stackoverflow.com/questions/2820234/can-someone-help-me-compare-using-f-over-c-in-this-specific-example-ip-address I was looking at the posted code and I was wondering if this code could be written without it producing a warning: let [|a;b;c;d|] = s.Split [|'.'|] IP(parseOrParts a, parseOrP...

Understanding pattern matching with cons operator

In "Programming F#" I came across a pattern-matching like this one (I simplified a bit): let rec len list = match list with | [] -> 0 | [_] -> 1 | head :: tail -> 1 + len tail;; Practically, I understand that the last match recognizes the head and tail of the list. Conceptually, I don't get why it works. As far as I understan...

Using sed with html data

I'm having some problems using sed in combination with html. The following sample illustrates the problem: HTML="<html><body>ENTRY</body><html>" TABLE="<table></table>" echo $HTML | sed -e s/ENTRY/$TABLE/ This outputs: sed: -e expression #1, char 18: unknown option to `s' If I leave out the / from $TABLE so that it becomes <table><...

[Erlang - trace] How to trace for all functions in an Erlang module except for one?

I wanted to trace for all functions in an erlang module, with dbg:tpl, but one of the internal functions took up 95% of the trace file. I then wanted to exclude only that single function and found that it was not as easy as I thought it would be. I know there are great pattern matching possibilities for arguments when tracing. Is ther...

In OpenRasta is it possible to Pattern match multiple key/value pairs?

Is it possible in OpenRasta to have a Uri pattern that allows for an array of values of the same key to be submitted and mapped to a handler method accepting an array of the query parameters. Example: Return all the contacts named Dave Smith from a collection. HTTP GET /contacts?filterBy=first&filterValue=Dave&filterBy=last&filterValue...

Replace whitespaces using PHP preg_replace function ignoring quoted strings

Look at the following string: SELECT column1 , column2, column3 FROM table1 WHERE column1 = 'text, "FROM" \'from\\\' x' AND column2 = "sample text 'where' \"where\\\" " AND ( column3 = 5 ) I need to escape unnecessary white space characters from the string like: removing white space from beginning and ending ...

scala 2.8.0.RC2 compiler problem on pattern matching statement?

Why does the following module not compile on Scala 2.8.RC[1,2]? object Test { import util.matching.Regex._ val pVoid = """\s*void\s*""".r val pVoidPtr = """\s*(const\s+)?void\s*\*\s*""".r val pCharPtr = """\s*(const\s+)GLchar\s*\*\s*""".r val pIntPtr = """\s*(const\s+)?GLint\s*\*\s*""".r val pUintPtr = """\s*(const\s+)?GLuint\s*\*\s*"...

What was the reason to choose the current syntax `import foo.bar.{Baz => _}` to exclude something from import?

I wonder if there is a good reason for this optical mismatch between e. g. pattern matching, which uses a simple case foo => to denote that no action should be taken. Wouldn't it be reasonable to have something like import foo.bar.{Baz => } instead of import foo.bar.{Baz => _} considering that _ is used as an "import everythin...

Implementing class for pattern matching

For example, val list = List(1,2,3) list match { case a :: b => case _ => } you can match head and tail of a List using :: or tokens of ParseResult using ~. What should I do to create class that can be matched like preceding classes? UPD: And have possibility to write: case class @ ... List(1,2,3,4) match { case 1 @ 2...

A maximum character limit on the preg functions?

On my site I use output buffering to grab all the output and then run it through a process function before sending it out to the browser (I don't replace anything, just break it into more manageable pieces). In this particular case, there is a massive amount of output because it is listing out a label for every country in the database (a...

How does pattern matching work behind the scenes in F#?

Hello Everyone, I am completely new to F# (and functional programming in general) but I see pattern matching used everywhere in sample code. I am wondering for example how pattern matching actually works? For example, I imagine it working the same as a for loop in other languages and checking for matches on each item in a collection. Th...

python grep reverse matching

Hi Alls, I would like to build a small python script that basicaly does the reverse of grep. I want to match the files in a directory/subdirectory that doesn't have a "searched_string". So far i've done that: import os filefilter = ['java','.jsp'] path= "/home/patate/code/project" for path, subdirs, files in os.walk(path): for ...

Regex for matching words, even though they might be words apart

So for the string: A large chicken, either thighs or breasts I need a regex to match the term "chicken breast" So it would be something like /chicken(.*?)breast/ would it not? Thanks. ...

f# pattern matching with DataGridColumn.Visibility

I'm encountering a situation where I'm using pattern matching for determining the visibility property of a column. System.Windows.Visibility has two fields, Visibility.Visible and Visibility.Collapsed. Can enyone tell me why the following code: let colItem = myDataGrid.Columns.Item 1 chkBox.IsChecked <- match colItem.V...

preg_match , pattern, php

I'm trying to extract some specific pictures from html content . Currently I have the following array [1] => Array ( [0] => BuEZm5g!Wk~$(KGrHqQH-DgEvrb2CLuOBL-vbkHlKw~~_14.JPG#!BuEZm5g!Wk~$(KGrHqQH-DgEvrb2CLuOBL-vbkHlKw~~_12.JPG|1#http://i.ebayimg.com/08#!BuEZqMQBGk~$(KGrHqQH-DoEvrKYSoPiBL-vb)WgLw~~_14.JPG#!BuEZ...

f# pattern matching with types

I'm trying to recursively print out all an objects properties and sub-type properties etc. My object model is as follows... type suggestedFooWidget = { value: float ; hasIncreasedSinceLastPeriod: bool ; } type firmIdentifier = { firmId: int ; firmName: string ; } type authorIdentifier = { authorId: int ; autho...

Pattern Matching with XSLT

I'm trying to match a pattern into a string in XSLT/XPath using the matches function, as follows: <xsl:when test="matches('awesome','awe')"> ... </xsl:when> However, in both Firefox 3.5.9 and IE8, it doesn't show up. IE8 tells me that "'matches' is not a valid XSLT or XPath function." Is this due to XSLT 2.0 not being supported, an...

Scala regex Named Capturing Groups

In scala.util.matching.Regex trait MatchData I see that there support for groupnames , I thought that this was related to (Regex Named Capturing Groups) But since Java does not support groupnames until version 7 as I understand it (ref), Scala version 2.8.0 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6. gives me this exception: scala>...

Matching of tuples

From what I understood I can use pattern-matching in a match ... with expression with tuples of values, so something like match b with ("<", val) -> if v < val then true else false | ("<=", val) -> if v <= val then true else false should be correct but it gives me a syntax error as if the parenthesis couldn't be used: File "oc...

how to to do the "noop but return unit" in OCaml

Hello, just a fast hint: I want to print a list of strings and I was going to do it by pattern matching just to get into this powerful functionality, how can I express the "do-nothing-but-return-unit" operation? What I mean is let print_nodes nodes = match nodes with [] -> (* here i want to noop *) | s :: t -> print_string s;...