Gray Soft / Tags / Style

25

SEP
2014

Regex Code Equivalency

#!/usr/bin/env ruby -w

Name = "Gray, James"

!!(Name =~ /\AGray/)      # => true
Name.start_with?("Gray")  # => true

!!(Name =~ /James\z/)    # => true
Name.end_with?("James")  # => true

!!(Name =~ /Dana/)     # => false
Name.include?("Dana")  # => false

!!(Name =~ /\A\z/)  # => false
Name.empty?         # => false

!!(Name =~ /\AGray, James\z/)  # => true
Name == "Gray, James"          # => true

!!(Name =~ /\A(?:Gray, James|Gray, Dana)\z/)  # => true
["Gray, James", "Gray, Dana"].include?(Name)  # => true

Name =~ /\A\w+/ && $&  # => "Gray"
Name[/\A\w+/]          # => "Gray"

Name =~ /\A(\w+),\s*(\w+)\z/ && $2  # => "James"
Name[/\A(\w+),\s*(\w+)\z/, 2]       # => "James"

Name =~ /\A(?<last>\w+),\s*(?<first>\w+)\z/ && $~[:first]  # => "James"
Name[/\A(?<last>\w+),\s*(?<first>\w+)\z/, :first]          # => "James"

Name.scan(/^.*\n?/)  # => ["Gray, James"]
Name.lines           # => ["Gray, James"]

Name.scan(/./m)  # => ["G", "r", "a", "y", ",", " ", "J", "a", "m", "e", "s"]
Name.chars       # => ["G", "r", "a", "y", ",", " ", "J", "a", "m", "e", "s"]

Name.gsub(/[aeiou]/, "")  # => "Gry, Jms"
Name.delete("aeiou")      # => "Gry, Jms"

Name.gsub(/[aeiou]/, "X") # => "GrXy, JXmXs"
Name.tr("aeiou", "X")     # => "GrXy, JXmXs"

# For the destructive operations that follow you can drop the `dup()` and
# switch `sub()` to `sub!()`, as long as you don't care about the return value.

Name.sub(/(?=,)/, " II")                 # => "Gray II, James"
Name.dup.insert(Name.index(","), " II")  # => "Gray II, James"

Name.sub(/\A/, "Name:  ")    # => "Name:  Gray, James"
Name.dup.prepend("Name:  ")  # => "Name:  Gray, James"

Name.sub(/\A.*\z/m, "Gray, Dana")  # => "Gray, Dana"
Name.dup.replace("Gray, Dana")     # => "Gray, Dana"

Name.sub(/\A.*\z/m, "")  # => ""
Name.dup.clear           # => ""



Spacey = "\tsome    space\r\n"

Spacey.sub(/\A\s+/, "")  # => "some    space\r\n"
Spacey.lstrip            # => "some    space\r\n"

Spacey.sub(/\s+\z/, "")  # => "\tsome    space"
Spacey.rstrip            # => "\tsome    space"

Spacey.sub(/\A\s*(.+?)\s*\z/m, '\1')  # => "some    space"
Spacey.strip                          # => "some    space"

Spacey.sub(/(?:\r?\n|\r)\z/m, "")  # => "\tsome    space"
Spacey.chomp                       # => "\tsome    space"

Spacey.sub(/(?:\r\n|.)\z/m, "")  # => "\tsome    space"
Spacey.chop                      # => "\tsome    space"

Spacey.gsub(/ +/, " ")  # => "\tsome space\r\n"
Spacey.squeeze(" ")     # => "\tsome space\r\n"

In: Deadly Regular Expressions | Tags: Regular Expression, Style & Syntax | 2 Comments

27

AUG
2014

I've mentioned before that I'm writing some Rust code, specifically an RPN calculator as a simple exercise. I'm going to dump the code here so we can discuss one aspect of it, but do remember that I'm very new to Rust and this code could surely be better:

use std::fmt;
use std::os;

struct Stack {
    numbers: Vec<f64>
}
impl Stack {
    fn new() -> Stack {
        Stack{numbers: vec![]}
    }

    fn is_empty(&self) -> bool {
        self.numbers.is_empty()
    }

    fn push(&mut self, number: f64) {
        self.numbers.push(number);
    }

    fn result(&self) -> f64 {
        *self.numbers.last().expect("Stack empty.")
    }

    fn add(&mut self)      { self._do_binary_operation(|l, r| l + r); }
    fn subtract(&mut self) { self._do_binary_operation(|l, r| l - r); }
    fn multiply(&mut self) { self._do_binary_operation(|l, r| l * r); }
    fn divide(&mut self)   { self._do_binary_operation(|l, r| l / r); }

    fn _do_binary_operation(&mut self, operation: |f64, f64| -> f64) {
        let r = self.numbers.pop().expect("Stack underflow.");
        let l = self.numbers.pop().expect("Stack underflow.");
        self.numbers.push(operation(l, r));
    }
}
impl fmt::Show for Stack {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut s = String::new();
        let mut i = self.numbers.len();
        for number in self.numbers.iter() {
            i -= 1;
            s = s.add(&format!("{}: {}\n", i, number));
        }
        s.pop_char();
        write!(f, "{}", s)
    }
}

struct Tokenizer {
    tokens: Vec<String>,
    i:      uint
}
impl Tokenizer {
    fn new(expression: &str) -> Tokenizer {
        Tokenizer{
          tokens: expression.split(|c: char| c.is_whitespace())
                            .map(|s| s.to_string())
                            .collect(),
          i:      0
        }
    }

    fn has_next_token(&self) -> bool {
        self.i < self.tokens.len()
    }

    fn next_token(&mut self) -> &str {
        if !self.has_next_token() { fail!("Tokens exhausted.") }

        let token = self.tokens[self.i].as_slice();
        self.i   += 1;
        token
    }
}

struct RPNCalculator {
    stack:  Stack,
    tokens: Tokenizer
}
impl RPNCalculator {
    fn new(stack: Stack, tokens: Tokenizer) -> RPNCalculator {
        RPNCalculator{stack: stack, tokens: tokens}
    }

    fn calculate(&mut self) -> f64 {
        while self.tokens.has_next_token() {
            let token = self.tokens.next_token();
            if !self.stack.is_empty() {
                println!("{}", self.stack);
            }
            println!("T: {}\n", token);
            match token {
                "+" => { self.stack.add(); }
                "-" => { self.stack.subtract(); }
                "*" => { self.stack.multiply(); }
                "/" => { self.stack.divide(); }
                n   => { self.stack.push(from_str(n).expect("Not a number.")); }
            }
        }
        if !self.stack.is_empty() {
            println!("{}\n", self.stack);
        }
        self.stack.result()
    }
}

fn main() {
    let     expression = os::args();
    let     stack      = Stack::new();
    let     tokenizer  = Tokenizer::new(expression[1].as_slice());
    let mut calculator = RPNCalculator::new(stack, tokenizer);
    println!("{}", calculator.calculate());
}