Pike (programming language)

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Pike is an interpreted, general-purpose, high-level, cross-platform, dynamic programming language, with a syntax similar to that of C. Unlike many other dynamic languages, Pike is both statically and dynamically typed, and requires explicit type definitions. It features a flexible type system that allows the rapid development and flexible code of dynamically typed languages, while still providing some of the benefits of a statically typed language.

Pike features garbage collection, advanced data types, and first-class anonymous functions, with support for many programming paradigms, including object-oriented, functional and imperative programming. Pike is free software, released under the GPL, LGPL and MPL licenses.

Contents

History

Pike has its roots in LPC, which was a language developed for MUDs. Programmers at Lysator in Linköping, Sweden, most notably Fredrik Hübinette and Per Hedbor, separated the language and virtual machine from the rest of the MUD driver, and used it as a rapid prototyping language for various applications, calling it LPC4. LPC's license did not allow use for commercial purposes, and so a new GPL implementation was written in 1994, called µLPC (micro LPC). In 1996, µLPC was renamed to Pike in order to provide a more commercially viable name. Although the name of the company has changed over the years, the company now known as Roxen Internet Software employed many Pike developers, and provided resources for Pike's development. Roxen is also the name of a web server developed by the company in Pike. In 2002, the programming environment laboratory at Linköping University took over maintenance of Pike from Roxen. Several Pike programmers have found their way to the Linköping office of Opera Software, where the language plays a central role in the server/gateway parts of the Opera Mini application.[1]

Syntax highlights

Hello World

int main() {
    write("Hello world!\n");
    return 0;
}

The syntax above requires some explanation. Those who are familiar with C or C++ should pick it up right away.

  • The first line contains the main function. This is the first function executed when a program starts. The "int" in front of it tells that a number of type Integer will be returned when the function ends.
  • The write function sends a string literal to the standard output buffer, which in most cases is a command line interface.
  • The third line returns a number to the caller of a function, in this case the command line interface where zero usually means the program executed without error.
  • The curly brackets enclose the function and the semicolon separates statements (meaning the function could have been written on a single line: int main(){write("Hello world!\n");return 0;})
  • The "\n" after "Hello world!" is a newline character.

[edit] Data types

The following list shows all the standard data types that Pike provides. Advanced data types such as sequences, queues, heaps, stacks, etc. are available in the ADT module which is included with Pike.

Basic data types:

  • int
  • float
  • string

Container types:

Other types:

  • program (the compiled representation of a class)
  • object (an instance of a class)
  • function

Pike requires explicit type definitions for all variables. It uses this information to report type errors at compile time. The following code will cause a compile error because the value of the variable "number" must be an integer but the code is attempting to assign floating point and string values to it.

int number;     // integer variable, it only accepts integers
number = 5.5;   // 5.5 is a floating point value, error
number = "5";   // "5" is a string, not the integer value 5, error

That kind of behavior is traditionally considered restrictive and limiting by proponents of dynamically typed languages. However unlike C, C++, and Java, Pike uses a more flexible type system—specifically, a system of tagged unions. The system allows programmers to declare variables that may contain values of multiple types, something impossible in most of the C-family languages without straying from the bounds of safe usage.

The following demonstrates a variable that can hold either an integer or a floating point number.

int|float number; // integer OR float variable
number = 5;       // this is legal
number = 5.5;     // this is legal also

Because a variable can be declared as holding many different data types, functions are provided to determine what type of data is currently stored. These functions are all of the form typenamep, as in intp, floatp, stringp, etc.

int|float number;
number = 5;
intp(number);      // returns true because number holds an int
floatp(number);    // returns false
number = 5.5;
floatp(number);    // returns true because number now holds a float

Additionally, there is a special "mixed" data type. That definition allows a variable to hold any kind of data type.

mixed anything;
anything = 5;    // anything is now the integer value 5
anything = 5.5;  // anything is now the float value 5.5
anything = "5";  // anything is now the string value "5"

In order to convert a value from one type to another, Pike can use an explicit cast:

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