#!/usr/bin/perl

# https://perlmonks.org/?node_id=11105353
# following spirit of my http://www.rosettacode.org/wiki/Compiler/lexical_analyzer#Alternate_Perl_Solution

use strict;
use warnings;

my @tokens;
my %reserved = map { $_ => 1 } qw(
  alignas alignof and and_eq asm atomic_cancel atomic_commit
  atomic_noexcept auto bitand bitor bool break case catch char
  char16_t char32_t class compl concept const constexpr const_cast
  continue co_await co_return co_yield decltype default delete do
  double dynamic_cast else enum explicit export extern false float for
  friend goto if import inline int long module mutable namespace new
  noexcept not not_eq nullptr operator or or_eq private protected
  public register reinterpret_cast requires return short signed
  sizeof static static_assert static_cast struct switch synchronized
  template this thread_local throw true try typedef typeid typename
  union unsigned using virtual void volatile wchar_t while xor xor_eq
  );
my %Character = ( # Single characters by name
        '(' => 'LeftParen',
        ')' => 'RightParen',
        '[' => 'LeftSquare',
        ']' => 'RightSquare',
        '{' => 'LeftCurly',
        '}' => 'RightCurly',
        '<' => 'LessThan',
        '>' => 'GreaterThan',
        '=' => 'Equal',
        '+' => 'Plus',
        '-' => 'Minus',
        '*' => 'Asterisk',
        '/' => 'Slash',
        '#' => 'Hash',
        '.' => 'Dot',
        ',' => 'Comma',
        ':' => 'Colon',
        ';' => 'Semicolon',
        "'" => 'SingleQuote',
        '"' => 'DoubleQuote',
        '|' => 'Pipe',
    );
my %MultiOps = (
  '>>' => 'RightShift',
  '<<' => 'LeftShift',
  '<=' => 'LessThanOrEqual',
  );
my $regex = qr/ \G (?|
  \s+                 (?{ undef })
  | \/\/.*            (?{ undef })
  | \d+(?:\.\d*)?     (?{ 'Number' })
  | \.\d+             (?{ 'Number' })
  | \w+               (?{ $reserved{$&} ? 'reserved' : 'Identifier' })
  | "([^"]*)"         (?{ [ 'string', $1 ] })
  | (?<!:)::(?!:)     (?{ 'dblColon' })
  | (?:<<|>>|<=)      (?{ $MultiOps{$&} })
  | .                 (?{ $Character{$&} or 'character' })
  ) /x;

$_ = join '', <DATA>;
defined $^R and push @tokens, ref $^R ? $^R : [ $^R, $& ] while /$regex/gc;
use Data::Dump 'dd'; dd @tokens;

__DATA__
// comment should not appear
main(void)
  {
  int foo = 1 << 5;
  puts("testing");
  exit(0); // done
  }

##</code><code>##

(
  ["Identifier", "main"],
  ["LeftParen", "("],
  ["reserved", "void"],
  ["RightParen", ")"],
  ["LeftCurly", "{"],
  ["reserved", "int"],
  ["Identifier", "foo"],
  ["Equal", "="],
  ["Number", 1],
  ["LeftShift", "<<"],
  ["Number", 5],
  ["Semicolon", ";"],
  ["Identifier", "puts"],
  ["LeftParen", "("],
  ["string", "testing"],
  ["RightParen", ")"],
  ["Semicolon", ";"],
  ["Identifier", "exit"],
  ["LeftParen", "("],
  ["Number", 0],
  ["RightParen", ")"],
  ["Semicolon", ";"],
  ["RightCurly", "}"],
)