Why can't Regular Expressions use keywords instead of characters?

Question

Okay, I barely understand RegEx basics, but why couldn't they design it to use keywords (like SQL) instead of some cryptic wildcard characters and symbols?

Is it for performance since the RegEx is interpreted/parsed at runtime? (not compiled)

Or maybe for speed of writing? Considering that when you learn some "simple" character combinations it becomes easier to type 1 character instead of a keyword?

Answer 1

You really want this?

Pattern findGamesPattern = Pattern.With.Literal(@"<div")
    .WhiteSpace.Repeat.ZeroOrMore
    .Literal(@"class=""game""").WhiteSpace.Repeat.ZeroOrMore.Literal(@"id=""")
    .NamedGroup("gameId", Pattern.With.Digit.Repeat.OneOrMore)
    .Literal(@"-game""")
    .NamedGroup("content", Pattern.With.Anything.Repeat.Lazy.ZeroOrMore)
    .Literal(@"<!--gameStatus")
    .WhiteSpace.Repeat.ZeroOrMore.Literal("=").WhiteSpace.Repeat.ZeroOrMore
    .NamedGroup("gameState", Pattern.With.Digit.Repeat.OneOrMore)
    .Literal("-->");

Ok, but it's your funeral, man.

Download the library that does this here:
http://flimflan.com/blog/ReadableRegularExpressions.aspx

Answer 2

Regular expressions have a mathematical (actually, language theory) background and are coded somewhat like a mathematical formula. You can define them by a set of rules, for example

• every character is a regular expression, representing itself
• if a and b are regular expressions, then a?, a|b and ab are regular expressions, too
• ...

Using a keyword-based language would be a great burden for simple regular expressions. Most of the time, you will just use a simple text string as search pattern:

grep -R 'main' *.c

Or maybe very simple patterns:

grep -c ':-[)(]' seidl.txt

Once you get used to regular expressions, this syntax is very clear and precise. In more complicated situations you will probably use something else since a large regular expression is obviously hard to read.