Euphoria - Quick Guide


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Euphoria - Overview

Euphoria stands for End-User Programming with Hierarchical Objects for Robust Interpreted Applications. Euphoria's first incarnation was created by Robert Craig on an Atari Mega-ST and it was first released in 1993. It is now maintained by Rapid Deployment Software.

It is a free, simple, flexible, easy to learn, and interpreted but extremely fast 32-bit high-level programming language for DOS, Windows, Linux, FreeBSD and more.

Euphoria is being used to develop Windows GUI programs, high-speed DOS games, and Linux/FreeBSD X Windows programs. Euphoria can also be used for CGI (Webbased) programming.

Euphoria Features

Here is the list of major features of Euphoria −

  • It is a simple, flexible, powerful language definition that is easy to learn and use.

  • It supports dynamic storage allocation which means variables grow or shrink without the programmer having to worry about allocating and freeing the memory. It takes care of garbage collection automatically.

  • It is extremely faster than conventional interpreters such as Perl and Python.

  • Euphoria programs run under Linux, FreeBSD, 32-bit Windows, and any DOS environment.

  • Euphoria programs are not subject to any 640K memory limitations.

  • It provides an optimizing Euphoria-To-C translator which you can use to translate your Euphoria program into C and then compile it with a C compiler to get an executable (.exe) file. This can boost your program speed by 2 to 5 times.

  • Underlying hardware are completely hidden which means programs are not aware of word-lengths, underlying bit-level representation of values, byte-order etc.

  • Euphoria installation comes along with a full-screen source debugger, an execution profiler, and a full-screen multi-file editor.

  • It supports run-time error-handling, subscript, and type checking.

  • It is an open source language and comes completely free of cost.

Platform Requirements

Euphoria is available on Windows, Linux, FreeBSD, and OSX. Here is the bare minimum version required with the following platforms −

  • WIN32 version − You need Windows 95 or any later version of Windows. It runs fine on XP and Vista.

  • Linux version − You need any reasonably up-to-date Linux distribution, that has libc6 or later. For example, Red Hat 5.2 or later works fine.

  • FreeBSD version − You need any reasonably up-to-date FreeBSD distribution.

  • Mac OS X version − You need any reasonably up-to-date Intel based Mac.

Euphoria Limitations

Here are some prominent limitations of Euphoria −

  • Even though Euphoria is simple, fast, and flexible enough for the programmers; it does not provide call support for many important functionalities. For example, network programming.

  • Euphoria was invented in 1993, and still you would not find any book written on this language. There is also not much documentation available for the language.

But these days, the language is getting popular very fast and you can hope to have nice utilities and books available for the language very soon.

Euphoria Licensing

This product is free and open source, and has benefited from the contributions of many people. You have complete royalty-free rights to distribute any Euphoria programs that you develop.

Icon files, such as euphoria.ico and binaries available in euphoria\bin, may be distributed with or without your changes.

You can shroud or bind your program and distribute the resulting files royalty-free. Some additional 3rd party legal restrictions might apply when you use the Euphoria- To-C translator.

The generous Open Source License allows Euphoria to use for both personal and commercial purposes. Unlike many other open source licenses, your changes do not have to be made open source.

Euphoria - Environment

This chapter describes about the installation of Euphoria on various platforms. You can follow the steps to install Euphoria on Linux, FreeBSD, and 32-bit Windows. So you can choose the steps based on your working environment.

Linux, Free BSD Installation

Official website provides .tar.gz file to install Euphoria on your Linux or BSD OS. You can download your latest version of Euphoria from its official website − Download Euphoria.

Once you have .tar.gz file, here are three simple steps to be performed to install Euphoria on your Linux or Free BSD machine −

Step 1 − Installing Files

Untar the downloaded file euphoria-4.0b2.tar.gz in a directory where you want to install Euphoria. If you want to install it in /home directory as follows, then −

$cp euphoria-4.0b2.tar.gz /home
$cd /home
$gunzip euphoria-4.0b2.tar.gz
$tar -xvf euphoria-4.0b2.tar

This creates a directory hierarchy inside /home/euphoria-4.0b2 directory as follows −

$ls -l
-rw-r--r-- 1 1001 1001 2485 Aug 17 06:15 Jamfile
-rw-r--r-- 1 1001 1001 5172 Aug 20 12:37 Jamrules
-rw-r--r-- 1 1001 1001 1185 Aug 13 06:21 License.txt
drwxr-xr-x 2 1001 1001 4096 Aug 31 10:07 bin
drwxr-xr-x 7 1001 1001 4096 Aug 31 10:07 demo
-rw-r--r-- 1 1001 1001 366 Mar 18 09:02 file_id.diz
drwxr-xr-x 4 1001 1001 4096 Aug 31 10:07 include
-rw-r--r-- 1 1001 1001 1161 Mar 18 09:02 installu.doc
drwxr-xr-x 4 1001 1001 4096 Aug 31 10:07 source
drwxr-xr-x 19 1001 1001 4096 Sep 7 12:09 tests
drwxr-xr-x 2 1001 1001 4096 Aug 31 10:07 tutorial

NOTE − File name euphoria-4.0b2.tar.gz depends on latest version available. We are using 4.0b2 version of the language for this tutorial.

Step 2 − Setting Up the Path

After installing Euphoria, you need to set proper paths so that your shell can find required Euphoria binaries and utilities. Before proceeding, there are following three important environment variables you need to set up −

  • Set PATH environment variable to point /home/euphoria-4.0b2/bin directory.

  • Set EUDIR environment variable to point to /home/euphoria-4.0b2.

  • Set EUINC environment variable to point to /home/euphoria-4.0b2/include.

These variables can be set as follows −

$export PATH=$PATH:/home/euphoria-4.0b2/bin
$export EUDIR=/home/euphoria-4.0b2
$export EUINC=/home/euphoria-4.0b2/include

NOTE − The above commands used to set environment variables may differ depending on your Shell. We used bash shell for executing these commands to set the variables.

Step 3 − Confirmation Installation

Confirm if you installed Euphoria successfully or not.

Execute the following command −

$eui -version

If you get following result, then it means you have installed Euphoria successfully; otherwise you have to go back and check all the steps again.

$eui -version
Euphoria Interpreter 4.0.0 beta 2 (r2670) for Linux
Using System Memory
$

That is it, Euphoria Programming Environment is ready on your UNIX machine, and you can start writing complex programs in easy steps.

WIN32, and DOS Installation

Official website provides .exe file to install Euphoria on your WIN32 or DOS OS. You can download your latest version of Euphoria from its official website − Download Euphoria.

Once you have .exe file, here are three simple steps to follow for installing Euphoria Programming language on your WIN32 or DOS machine −

Step 1 − Installing Files

Double click on the downloaded .exe setup program to install all the files. We downloaded euphoria-40b2.exe file for installation.

The filename euphoria-40b2.exe depends on latest version available. We use version 4 beta 2 of the language.

By default Euphoria would be installed in C:\euphoria-40b2 directory but you can also select a desired location.

Step 2 − Rebooting the Machine

Re-boot your machine to complete the installation.

Step 3 − Confirmation Installation

Confirm if you installed Euphoria successfully or not.

Execute the following command −

c:\>eui -version

If you get following result, then it means you have installed Euphoria successfully; otherwise you have to go back and check all the steps again.

c:\>eui -version
Euphoria Interpreter 4.0.0 beta 2 (r2670) for Windows
Using Managed Memory

c:\>

That is it, Euphoria Programming Environment is ready on your WIN32 machine, and you can start writing complex programs in easy steps.

Euphoria Interpreters

Depending on the platform you are using, Euphoria has multiple interpreters −

  • The main interpreter is eui.

  • On windows platforms, you have two choices. If you run eui then a console window is created. If you run euiw then no console is created, making it suitable for GUI applications.

  • Euphoria does not care about your choice of file extensions. By convention however; the console-based applications come with .ex extension.

  • GUI-based applications have .exw extension and the include files have .e extension.

Euphoria - Basic Syntax

The Euphoria language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages. This chapter is designed to quickly get you up to speed on the syntax that is expected in Euphoria.

This tutorial assumes you are working with Linux and all the examples have been written on Linux platform. But it is observed that there is no any prominent difference in program syntax on Linux and WIN32. Hence you can follow the same steps on WIN32.

First Euphoria Program

Let us write a simple Euphoria program in a script. Type the following source code in test.ex file and save it.

#!/home/euphoria-4.0b2/bin/eui

puts(1, "Hello, Euphoria!\n")

Let us say, Euphoria interpreter is available in /home/euphoria-4.0b2/bin/ directory. Now run this program as follows −

$ chmod +x test.ex    # This is to make file executable
$ ./test.ex

This produces the following result −

Hello, Euphoria!

This script used a built-in function puts() which takes two arguments. First argument indicates file name or device number, and second argument indicates a string which you want to print. Here 1 indicates STDOUT device.

Euphoria Identifiers

A Euphoria identifier is a name used to identify a variable, function, class, module, or other object. An identifier starts with a letter A to Z or a to z and then followed by letters, digits, or underscores.

Euphoria does not allow punctuation characters such as @, $, and % within identifiers.

Euphoria is a case sensitive programming language. Thus Manpower and manpower are two different identifiers in Euphoria. For example, the valid identifiers are −

  • n
  • color26
  • ShellSort
  • quick_sort
  • a_very_long_indentifier

Reserved Words

The following list shows the reserved words in Euphoria. These reserved words may not be used as constant or variable or any other identifier names. Euphoria keywords contain lowercase letters only.

and exit override
as export procedure
break fallthru public
by for retry
case function return
constant global routine
continue goto switch
do if then
else ifdef to
elsedef include type
elsif label until
elsifdef loop while
end namespace with
entry not without
enum or xor

Expressions

Euphoria lets you calculate results by forming expressions. However, in Euphoria you can perform calculations on entire sequences of data with one expression.

You can handle a sequence much as you would handle a single number. It can be copied, passed to a subroutine, or calculated upon as a unit. For example −

{1,2,3} + 5

This is an expression that adds the sequence {1, 2, 3} and the atom 5 to get the resulting sequence {6, 7, 8}. You would learn sequences in subsequent chapters.

Blocks of code

One of the first caveats programmers encounter when learning Euphoria is the fact that there are no braces to indicate blocks of code for procedure and function definitions or flow control. Blocks of code are denoted by associated keywords.

The following example shows if...then...end if block −

if condition then
   code block comes here
end if

Multi-Line Statements

Statements in Euphoria typically end with a new line. Euphoria does however, allow to write a single statement in multiple lines. For example −

total = item_one + 
   item_two + 
   item_three

Escape Characters

Escape characters may be entered using a back-slash. For example −

The following table is a list of escape or non-printable characters that can be represented with backslash notation.

Backslash notation Description
\n Newline
\r Carriage return
\t Tab
\\ Backslash
\" Double quote
\' Single quote

Comments in Euphoria

Any comments are ignored by the compiler and have no effect on execution speed. It is advisable to use more comments in your program to make it more readable.

There are three forms of comment text −

  • Comments start by two dashes and extend to the end of the current line.

  • The multi-line format comment is kept inside /*...*/, even if that occurs on a different line.

  • You can use a special comment beginning with the two character sequence “#!” only on the first line of the program.

Examples

#!/home/euphoria-4.0b2/bin/eui
-- First comment
puts(1, "Hello, Euphoria!\n") -- second comment

/* This is a comment which extends over a number
   of text lines and has no impact on the program
*/

This produces the following result −

Hello, Euphoria!

Note − You can use a special comment beginning with “#!”. This informs the Linux shell that your file should be executed by the Euphoria interpreter.

Euphoria - Variables

Variables are nothing but reserved memory locations to store values. This means when you create a variable, you reserve some space in memory.

Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables. Euphoria data types are explained in different chapter.

These memory locations are called variables because their value can be changed during their life time.

Variable Declaration

Euphoria variables have to be explicitly declared to reserve memory space. Thus declaration of a variable is mandatory before you assign a value to a variable.

Variable declarations have a type name followed by a list of the variables being declared. For example −

integer x, y, z

sequence a, b, x

When you declare a variable, you name the variable and you define which sort of values may legally be assigned to the variable during execution of your program.

The simple act of declaring a variable does not assign any value to it. If you attempt to read it before assigning any value to it, Euphoria will issue a run-time error as "variable xyz has never been assigned a value".

Assigning Values

The equal sign (=) is used to assign values to variables. Variable can be assigned in the following manner −

Variable_Name = Variable_Value

For example −

#!/home/euphoria/bin/eui

-- Here is the declaration of the variables.
integer counter
integer miles
sequence name

counter = 100 -- An integer assignment
miles = 1000.0 -- A floating point
name = "John" -- A string ( sequence )

printf(1, "Value of counter %d\n", counter )
printf(1, "Value of miles %f\n", miles )
printf(1, "Value of name %s\n", {name} )

Here 100, 1000.0 and "John" are the values assigned to counter, miles and name variables, respectively. This program produces the following result −

Value of counter 100
Value of miles 1000.000000
Value of name John

To guard against forgetting to initialize a variable, and also because it may make the code clearer to read, you can combine declaration and assignment −

integer n = 5

This is equivalent to the following −

integer n
n = 5

Identifier Scope

The scope of an identifier is a description of what code can access it. Code in the same scope of an identifier can access that identifier and code not in the same scope as identifier cannot access it.

The scope of a variable depends upon where and how it is declared.

  • If it is declared within a for, while, loop or switch, its scope starts at the declaration and ends at the respective end statement.

  • In an if statement, the scope starts at the declaration and ends either at the next else, elsif or end if statement.

  • If a variable is declared within a routine, the scope of the variable starts at the declaration and ends at the routine's end statement. This is knows as a private variable.

  • If a variable is declared outside of a routine, its scope starts at the declaration and ends and the end of the file it is declared in. This is known as a module variable.

  • The scope of a constant that does not have a scope modifier, starts at the declaration and ends and the end of the file it is declared in.

  • The scope of a enum that does not have a scope modifier, starts at the declaration and ends and the end of the file it is declared in.

  • The scope of all procedures, functions and types, which do not have a scope modifier, starts at the beginning of the source file and ends at the end of the source file in which they are declared.

Constants, enums, module variables, procedures, functions and types, which do not have a scope modifier are referred to as locals. However, these identifiers can have a scope modifier preceding their declaration, which causes their scope to extend beyond the file they are declared in.

  • If the keyword global precedes the declaration, the scope of these identifiers extends to the whole application. They can be accessed by code anywhere in the application files.

  • If the keyword public precedes the declaration, the scope extends to any file that explicitly includes the file in which the identifier is declared, or to any file that includes a file that in turn public includes the file containing the public declaration.

  • If the keyword export precedes the declaration, the scope only extends to any file that directly includes the file in which the identifier is declared.

When you include a Euphoria file in another file, only the identifiers declared using a scope modifier are accessible to the file doing the include. The other declarations in the included file are invisible to the file doing the include.

Euphoria - Constants

Constants are also variables that are assigned an initial value that can never change in the program’s life. Euphoria allows to define constants using constant keyword as follows −

constant MAX = 100
constant Upper = MAX - 10, Lower = 5
constant name_list = {"Fred", "George", "Larry"}

The result of any expression can be assigned to a constant, even one involving calls to previously defined functions, but once the assignment is made, the value of the constant variable is "locked in".

Constants may not be declared inside a subroutine. The scope of a constant that does not have a scope modifier, starts at the declaration and ends and the end of the file it is declared in.

Examples

#!/home/euphoria-4.0b2/bin/eui

constant MAX = 100
constant Upper = MAX - 10, Lower = 5

printf(1, "Value of MAX %d\n", MAX )
printf(1, "Value of Upper %d\n", Upper )
printf(1, "Value of Lower %d\n", Lower )

MAX = MAX + 1
printf(1, "Value of MAX %d\n", MAX )

This produces the following error −

./test.ex:10
<0110>:: may not change the value of a constant
MAX = MAX + 1
   ^

Press Enter

If you delete last two lines from the example, then it produces the following result −

Value of MAX 100
Value of Upper 90
Value of Lower 5

The enums

An enumerated value is a special type of constant where the first value defaults to the number 1 and each item after that is incremented by 1. Enums can only take numeric values.

Enums may not be declared inside a subroutine. The scope of an enum that does not have a scope modifier, starts at the declaration and ends and the end of the file it is declared in.

Examples

#!/home/euphoria-4.0b2/bin/eui

enum ONE, TWO, THREE, FOUR

printf(1, "Value of ONE %d\n", ONE )
printf(1, "Value of TWO %d\n", TWO )
printf(1, "Value of THREE %d\n", THREE )
printf(1, "Value of FOUR %d\n", FOUR )

This will produce following result −

Value of ONE 1
Value of TWO 2
Value of THREE 3
Value of FOUR 4

You can change the value of any one item by assigning it a numeric value. Subsequent values are always the previous value plus one, unless they too are assigned a default value.

#!/home/euphoria-4.0b2/bin/eui

enum ONE, TWO, THREE, ABC=10, XYZ

printf(1, "Value of ONE %d\n", ONE )
printf(1, "Value of TWO %d\n", TWO )
printf(1, "Value of THREE %d\n", THREE )
printf(1, "Value of ABC %d\n", ABC )
printf(1, "Value of XYZ %d\n", XYZ )

This produce the following result −

Value of ONE 1
Value of TWO 2
Value of THREE 3
Value of ABC 10
Value of XYZ 11

Sequences use integer indices, but with enum you may write code like this −

enum X, Y
sequence point = { 0,0 }

point[X] = 3
point[Y] = 4

Euphoria - Data Types

The data stored in memory can be of many types. For example, a person's age is stored as a numeric value and his or her address is stored as alphanumeric characters.

Euphoria has some standard types that are used to define the operations possible on them and the storage method for each of them.

Euphoria has following four standard data types −

  • integer
  • atom
  • sequence
  • object

The understanding of atoms and sequences is the key to understanding Euphoria.

Integers

Euphoria integer data types store numeric values. They are declared and defined as follows −

integer var1, var2

var1 = 1
var2 = 100

The variables declared with type integer must be atoms with integer values from -1073741824 to +1073741823 inclusive. You can perform exact calculations on larger integer values, up to about 15 decimal digits, but declare them as atom, rather than integer.

Atoms

All data objects in Euphoria are either atoms or sequences. An atom is a single numeric value. Atoms can have any integer or double-precision floating point value. Euphoria atoms are declared and defined as follows−

atom var1, var2, var3

var1 = 1000
var2 = 198.6121324234
var3 = 'E'       

The atoms can range from approximately -1e300 to +1e300 with 15 decimal digits of accuracy. An individual character is an atom which must may be entered using single quotes. For example, all the following statements are legal −

-- Following is equivalent to the atom 66 - the ASCII code for B
char = 'B'

-- Following is equivalent to the sequence {66}
sentence = "B"

Sequences

A sequence is a collection of numeric values which can be accessed through their index. All data objects in Euphoria are either atoms or sequences.

Sequence index starts from 1 unlike other programming languages where array index starts from 0. Euphoria sequences are declared and defined as follows −

sequence var1, var2, var3, var4

var1 = {2, 3, 5, 7, 11, 13, 17, 19}
var2 = {1, 2, {3, 3, 3}, 4, {5, {6}}}
var3 = {{"zara", "ali"}, 52389, 97.25}     
var4 = {} -- the 0 element sequence

A character string is just a sequence of characters which may be entered using double quotes. For example, all the following statements are legal −

word = 'word'
sentence = "ABCDEFG"

Character strings may be manipulated and operated upon just like any other sequences. For example, the above string is entirely equivalent to the sequence −

sentence = {65, 66, 67, 68, 69, 70, 71}

You will learn more about sequence in Euphoria − Sequences.

Objects

This is a super data type in Euphoria which may take on any value including atoms, sequences, or integers. Euphoria objects are declared and defined as follows −

object var1, var2, var3

var1 = {2, 3, 5, 7, 11, 13, 17, 19}
var2 = 100
var3 = 'E'     

An object may have one of the following values −

  • a sequence

  • an atom

  • an integer

  • an integer used as a file number

  • a string sequence, or single-character atom

Euphoria - Operators

Euphoria provides a rich set of operators to manipulate variables. We can divide all the Euphoria operators into the following groups −

  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Assignment Operators
  • Misc Operators

The Arithmetic Operators

Arithmetic operators are used in mathematical expressions in the same way that they are used in Algebra. The following table lists the arithmetic operators. Assume integer variable A holds 10 and variable B holds 20 then −

Show Examples

Operator Description Example
+ Addition - Adds values on either side of the operator A + B will give 30
- Subtraction - Subtracts right hand operand from left hand operand A - B will give -10
* Multiplication - Multiplies values on either side of the operator A * B will give 200
/ Division - Divides left hand operand by right hand operand B / A will give 2
+ Unary plus - This has no impact on the variable value. +B gives 20
- Unary minus - This creates a negative value of the given variable. -B gives -20

The Relational Operators

There are following relational operators supported by Euphoria language. Assume variable A holds 10 and variable B holds 20 then −

Show Examples

Operator Description Example
= Checks if the value of two operands are equal or not, if yes then condition becomes true. (A = B) is not true.
!= Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true.
> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true.
< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true.
>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true.
<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.

The Logical Operators

The following table lists the logical operators. Assume boolean variables A holds 1 and variable B holds 0 then −

Show Examples

Operator Description Example
and Called Logical AND operator. If both the operands are non zero then then condition becomes true. (A and B) is false.
or Called Logical OR Operator. If any of the two operands are non zero then then condition becomes true. (A or B) is true.
xor Called Logical XOR Operator. Condition is true if one of them is true, if both operands are true or false then condition becomes false. (A xor B) is true.
not Called Logical NOT Operator which negates the result. Using this operator, true becomes false and false becomes true not(B) is true.

You can also apply these operators to numbers other than 1 or 0. The convention is: zero means false and non-zero means true.

The Assignment Operators

There are following assignment operators supported by Euphoria language −

Show Examples

Operator Description Example
= Simple assignment operator, Assigns values from right side operands to left side operand C = A + B will assigne value of A + B into C
+= Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand C += A is equivalent to C = C + A
-= Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand C -= A is equivalent to C = C - A
*= Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand C *= A is equivalent to C = C * A
/= Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand C /= A is equivalent to C = C / A
&= Concatenation operator C &= {2} is same as C = {C} & {2}

Note − The equals symbol '=' used in an assignment statement is not an operator, it is just a part of the syntax.

Miscellaneous Operators

There are few other operators supported by Euphoria Language.

The '&' Operator

Any two objects may be concatenated using “&” operator. The result is a sequence with a length equal to the sum of the lengths of the concatenated objects.

For example −

#!/home/euphoria-4.0b2/bin/eui

sequence a, b, c
a = {1, 2, 3}
b = {4}
c = {1, 2, 3} & {4}

printf(1, "Value of c[1] %d\n", c[1] )
printf(1, "Value of c[2] %d\n", c[2] )
printf(1, "Value of c[3] %d\n", c[3] )
printf(1, "Value of c[4] %d\n", c[4] )

This produces the following result −

Value of c[1] 1
Value of c[2] 2
Value of c[3] 3
Value of c[4] 4

Precedence of Euphoria Operators

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.

For example, x = 7 + 3 * 2

Here, x is assigned 13, not 20 because operator * has higher precedence than +.

Hence it first starts with 3*2 and then adds into 7.

Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators is evaluated first.

Category Operator Associativity
Postfix function/type calls  
Unary + - ! not Right to left
Multiplicative * / Left to right
Additive + - Left to right
Concatenation & Left to right
Relational > >= < <= Left to right
Equality = != Left to right
Logical AND and Left to right
Logical OR or Left to right
Logical XOR xor Left to right
Comma , Left to right

Euphoria - Branching

Branching is the most important aspect of any programming language. While writing your program, you may encounter a situation when you have to take a decision or you have to select one option out of the given many options.

Following diagram shows a simple scenario where a program needs to take one of the two paths based on the given condition.

Branching

Euphoria provides following three types of decision making (branching or conditional) statements −

Let us see the statements in detail −

Euphoria - Loop Types

Looping is yet another most important aspect of any programming language. While writing your program, you may encounter a situation when you have to execute same statement many times and sometime may be infinite number of times.

There are several ways to specify for how long the process should go on, and how to stop or otherwise alter it. An iterative block may be informally called a loop, and each execution of code in a loop is called an iteration of the loop.

The following diagram shows a simple logical flow of a loop −

Looping

Euphoria provides following three types of loop statements −

All the above statements provide you flexibility and ease of use based on different situations. Let us see them in detail one by one −

Euphoria - Flow Control

Program execution flow refers to the order in which program statements get executed. By default the statements get executed one after another.

However; many times the order of execution needs to be altered from the default order, to get the task done.

Euphoria has a number of flow control statements that you can use to arrange the execution order of statements.

The exit statement

Exiting a loop is done with the keyword exit. This causes flow to immediately leave the current loop and recommence with the first statement after the end of the loop.

Syntax

The syntax of an exit statement is as follows −

exit [ "Label Name" ] [Number]

The exit statement terminates the latest and innermost loop until an optional label name or number is specified.

A special form of exit N is exit 0. This leaves all levels of loop, regardless of the depth. Control continues after the outermost loop block. Likewise, exit -1 exits the second outermost loop, and so on.

Example

#!/home/euphoria-4.0b2/bin/eui

integer b

for a = 1 to 16 do
   printf(1, "value of a %d\n", a)
   
   if a = 10 then
      b = a
      exit
   end if
end for

printf(1, "value of b %d\n", b)

This produces the following result −

value of a 1
value of a 2
value of a 3
value of a 4
value of a 5
value of a 6
value of a 7
value of a 8
value of a 9
value of a 10
value of b 10

The break statement

The break statement works exactly like the exit statement, but applies to if statements or switch statements rather than to loop statements of any kind.

Syntax

The syntax of break statement is as follows −

break [ "Label Name" ] [Number]

The break statement terminates the latest and innermost if or switch block until an optional label name or number is specified.

A special form of break N is break 0. This leaves the outer most if or switch block, regardless of the depth. Control continues after the outermost block. Likewise, break -1 breaks the second outermost if or switch block, and so on.

Example

#!/home/euphoria-4.0b2/bin/eui

integer a, b
sequence s = {'E','u', 'p'}

if s[1] = 'E' then
   a = 3
   
   if s[2] = 'u' then
      b = 1
      if s[3] = 'p' then
         break 0 -- leave topmost if block
      end if
      a = 2
   else
      b = 4
   end if
else
   a = 0
   b = 0
end if

printf(1, "value of a %d\n", a)
printf(1, "value of b %d\n", b)

This produces the following result −

value of a 3
value of b 1

The continue statement

The continue statement continues execution of the loop it applies to by going to the next iteration and skipping the rest of an iteration.

Going to the next iteration means testing a condition variable index and checking whether it is still within bounds.

Syntax

The syntax of continue statement is as follows −

continue [ "Label Name" ] [Number]

The continue statement would re-iterate the latest and inner most loop until an optional label name or number is specified.

A special form of continue N is continue 0. This re-iterate the outer most loop, regardless of the depth. Likewise, continue -1 starts from the second outermost loop, and so on.

Example

#!/home/euphoria-4.0b2/bin/eui

for a = 3 to 6 do
   printf(1, "value of a %d\n", a)

   if a = 4 then
      puts(1,"(2)\n")
      continue
   end if

   printf(1, "value of a %d\n", a*a)
end for
This would produce following result:

value of a 3
value of a 9
value of a 4
(2)
value of a 5
value of a 25
value of a 6
value of a 36

The retry statement

The retry statement continues execution of the loop it applies to by going to the next iteration and skipping the rest of an iteration.

Syntax

The syntax of retry statement is as follows −

retry [ "Label Name" ] [Number]

The retry statement retries executing the current iteration of the loop it applies to. The statement branches to the first statement of the designated loop neither testing anything nor incrementing the for loop index.

A special form of retry N is retry 0. This retries executing the outer most loop, regardless of the depth. Likewise, retry -1 retries the second outermost loop, and so on.

Normally, a sub-block which contains a retry statement also contains another flow control keyword like exit, continue, or break. Otherwise, the iteration would be endlessly executed.

Example

#!/home/euphoria-4.0b2/bin/eui

integer errors = 0
integer files_to_open = 10

for i = 1 to length(files_to_open) do
   fh = open(files_to_open[i], "rb")
   
   if fh = -1 then
      if errors > 5 then
         exit
      else
         errors += 1
         retry
      end if
   end if
   file_handles[i] = fh
end for

Since retry does not change the value of i and tries again opening the same file, there has to be a way to break from the loop, which the exit statement provides.

The goto statement

The goto statement instructs the computer to resume code execution at a labeled place.

The place to resume execution is called the target of the statement. It is restricted to lie in the current routine, or the current file if outside any routine.

Syntax

The syntax of goto statement is as follows −

goto "Label Name"

The target of a goto statement can be any accessible label statement −

label "Label Name"

Label names must be double quoted constant strings. Characters that are illegal in Euphoria identifiers may appear in a label name, since it is a regular string.

Example

#!/home/euphoria-4.0b2/bin/eui

integer a = 0

label "FIRST"
printf(1, "value of a %d\n", a)
a += 10

if a < 50 then
   goto "FIRST"
end if 
printf(1, "Final value of a %d\n", a)

This produces the following result −

value of a 0
value of a 10
value of a 20
value of a 30
value of a 40
Final value of a 50

Euphoria - Short Circuit Evaluation

When a condition is tested by if, elsif, until, or while using and or or operators, a short-circuit evaluation is used. For example −

if a < 0 and b > 0 then
   -- block of code
end if

If a < 0 is false, then Euphoria does not bother to test if b is greater than 0. It knows that the overall result is false regardless. Similarly −

if a < 0 or b > 0 then
   -- block of code
end if

if a < 0 is true, then Euphoria immediately decides that the result true, without testing the value of b, since the result of this test is irrelevant.

In General, whenever you have a condition of the following form −

A and B

Where A and B can be any two expressions, Euphoria takes a short-cut when A is false and immediately makes the overall result false, without even looking at expression B.

Similarly, whenever you have a condition of the following form −

A or  B

Where A is true, Euphoria skips the evaluation of expression B, and declares the result to be true.

Short-circuit evaluation of and and or takes place for if, elsif, until, and while conditions only. It is not used in other contexts. For example −

x = 1 or {1,2,3,4,5} -- x should be set to {1,1,1,1,1}

If short-circuiting were used here, you would set x to 1, and not even look at {1,2,3,4,5}, which would be wrong.

Thus, short-circuiting can be used in if, elsif, until, or while conditions, because you need to only care if the result is true or false, and conditions are required to produce an atom as a result.

Euphoria - Sequences

A sequence is represented by a list of objects in brace brackets { }, separated by commas. A sequence can contain both atoms and other sequences. For example −

{2, 3, 5, 7, 11, 13, 17, 19}
{1, 2, {3, 3, 3}, 4, {5, {6}}}
{{"Zara", "Ayan"}, 52389, 97.25}
{} -- the 0-element sequence

A single element of a sequence may be selected by giving the element number in square brackets. Element numbers start at 1.

For example, if x contains {5, 7.2, 9, 0.5, 13} then x[2] is 7.2.

Suppose x[2] contains {11,22,33}, Now if you ask for x[2] you get {11,22,33} and if you ask for x[2][3], you get the atom 33.

Example

#!/home/euphoria-4.0b2/bin/eui

sequence x
x = {1, 2, 3, 4}

for a = 1 to length(x) do
   printf(1, "value of x[%d] = %d\n", {a, x[a]})
end for

Here, length() is the built-in function which returns length of the sequence. The above example produces the following result −

value of x[1] = 1
value of x[2] = 2
value of x[3] = 3
value of x[4] = 4

Character String

A character string is just a sequence of characters. It may be entered in one of the two ways −

(a) Using Double Quotes −

"ABCDEFG"

(b) Using Raw String Notation −

-- Using back-quotes
`ABCDEFG`

or

-- Using three double-quotes
"""ABCDEFG"""

You can try the following example to understand the concept −

#!/home/euphoria-4.0b2/bin/eui

sequence x
x = "ABCD"

for a = 1 to length(x) do
   printf(1, "value of x[%d] = %s\n", {a, x[a]})
end for

This produces the following result −

value of x[1] = A
value of x[2] = B
value of x[3] = C
value of x[4] = D

String Arrays

An array of strings can be implemented using Sequences as follows −

#!/home/euphoria-4.0b2/bin/eui

sequence x = {"Hello", "World", "Euphoria", "", "Last One"}

for a = 1 to length(x) do
   printf(1, "value of x[%d] = %s\n", {a, x[a]})
end for

This produces the following result −

value of x[1] = Hello
value of x[2] = World
value of x[3] = Euphoria
value of x[4] =
value of x[5] = Last One

Euphoria Structures

A structure can be implemented using Sequences as follows −

#!/home/euphoria-4.0b2/bin/eui

sequence employee = {
   {"John","Smith"},
      45000,
      27,
      185.5
}
printf(1, "First Name = %s, Last Name = %s\n", {employee[1][1],employee[1][2]} )

This produces the following result −

First Name = John, Last Name = Smith

There are various operations which can be performed directly on sequences. Let us see them in detail −

Urinary Operation

When applied to a sequence, a unary operator is actually applied to each element in the sequence to yield a sequence of results of the same length.

#!/home/euphoria-4.0b2/bin/eui

sequence x
x = -{1, 2, 3, 4}

for a = 1 to length(x) do
   printf(1, "value of x[%d] = %d\n", {a, x[a]})
end for

This produces the following result −

value of x[1] = -1
value of x[2] = -2
value of x[3] = -3
value of x[4] = -4

Arithmetic Operations

Almost all arithmetic operations can be performed on sequences as follows −

#!/home/euphoria-4.0b2/bin/eui

sequence x, y, a, b, c
x = {1, 2, 3}
y = {10, 20, 30}

a = x + y
puts(1, "Value of a = {")

for i = 1 to length(a) do
   printf(1, "%d,", a[i])
end for
puts(1, "}\n")

b = x - y
puts(1, "Value of b = {")
for i = 1 to length(a) do
   printf(1, "%d,", b[i])
end for
puts(1, "}\n")

c = x * 3
puts(1, "Value of c = {")

for i = 1 to length(c) do
   printf(1, "%d,", c[i])
end for
puts(1, "}\n")

This produces the following result −

Value of a = {11,22,33,}
Value of b = {-9,-18,-27,}
Value of c = {3,6,9,}

Command Line Options

A user can pass command line options to a Euphoria script and it can be accessed as a sequence using command_line() function as follows −

#!/home/euphoria-4.0b2/bin/eui

sequence x

x = command_line()

printf(1, "Interpeter Name: %s\n", {x[1]} )
printf(1, "Script Name: %s\n", {x[2]} )
printf(1, "First Argument: %s\n", {x[3]})
printf(1, "Second Argument: %s\n", {x[4]})

Here printf() is Euphoria's built-in function. Now if you run this script as follows −

$eui test.ex "one" "two"

This produces the following result −

Interpeter Name: /home/euphoria-4.0b2/bin/eui
Script Name: test.ex
First Argument: one
Second Argument: two

Euphoria - Date & Time

Euphoria has a library routine that returns the date and time to your program.

The date() Method

The date() method returns a sequence value composed of eight atom elements. The following example explains it in detail −

#!/home/euphoria-4.0b2/bin/eui
 
integer curr_year, curr_day, curr_day_of_year, curr_hour, curr_minute, curr_second
sequence system_date, word_week, word_month, notation, 
   curr_day_of_week, curr_month
   word_week = {"Sunday", 
      "Monday", 
      "Tuesday", 
      "Wednesday", 
      "Thursday", 
      "Friday", 
      "Saturday"}
   word_month = {"January", "February", 
      "March", 
      "April", 
      "May", 
      "June", 
      "July", 
      "August", 
      "September", 
      "October", 
      "November", 
      "December"}
-- Get current system date.
system_date = date()

-- Now take individual elements
curr_year = system_date[1] + 1900
curr_month = word_month[system_date[2]]
curr_day = system_date[3]
curr_hour = system_date[4]
curr_minute = system_date[5]
curr_second = system_date[6]
curr_day_of_week = word_week[system_date[7]]
curr_day_of_year = system_date[8]

if curr_hour >= 12 then 
   notation = "p.m."
else 
   notation = "a.m."
end if

if curr_hour > 12 then 
   curr_hour = curr_hour - 12
end if

if curr_hour = 0 then 
   curr_hour = 12
end if

puts(1, "\nHello Euphoria!\n\n")
printf(1, "Today is %s, %s %d, %d.\n", {curr_day_of_week, 
   curr_month, curr_day, curr_year})

printf(1, "The time is %.2d:%.2d:%.2d %s\n", {curr_hour, 
   curr_minute, curr_second, notation})

printf(1, "It is %3d days into the current year.\n", {curr_day_of_year})

This produces the following result on your standard screen −

Hello Euphoria!

Today is Friday, January 22, 2010.
The time is 02:54:58 p.m.
It is  22 days into the current year.

The time() Method

The time() method returns an atom value, representing the number of seconds elapsed since a fixed point in time. The following example explains it in detail −

#!/home/euphoria-4.0b2/bin/eui
 
constant ITERATIONS = 100000000
integer p
atom t0, t1, loop_overhead

t0 = time()
for i = 1 to ITERATIONS do
   -- time an empty loop
end for

loop_overhead = time() - t0

printf(1, "Loop overhead:%d\n", loop_overhead)

t0 = time()
for i = 1 to ITERATIONS do
    p = power(2, 20)
end for

t1 = (time() - (t0 + loop_overhead))/ITERATIONS

printf(1, "Time (in seconds) for one call to power:%d\n", t1)

This produces the following result −

Loop overhead:1
Time (in seconds) for one call to power:0

Date & Time Related Methods

Euphoria provides a list of methods which helps you in manipulating date and time. These methods are listed in Euphoria Library Routines.

Euphoria - Procedures

A procedure is a group of reusable code which can be called from anywhere in your program. This eliminates the need of writing same code again and again. This helps programmers to write modular code.

Like any other advance programming language, Euphoria also supports all the features necessary to write modular code using procedures.

You must have seen procedures like printf() and length() in previous chapters. We are using these procedure again and again but they have been written in core Euphoria only once.

Euphoria allows you to write your own procedures as well. This section explains how to write your own procedure in Euphoria.

Procedure Definition

Before you use a procedure, you need to define it. The most common way to define a procedure in Euphoria is by using the procedure keyword, followed by a unique procedure name, a list of parameters (that might be empty), and a statement block which ends with end procedure statement. The basic syntax is as shown below −

procedure procedurename(parameter-list)

   statements
   ..........

end procedure

Example

A simple procedure called sayHello that takes no parameters is defined here −

procedure  sayHello()
   puts(1, "Hello there")
end procedure

Calling a Procedure

To invoke a procedure somewhere later in the script, you simply need to write the name of that procedure as follows −

#!/home/euphoria-4.0b2/bin/eui

procedure  sayHello()
   puts(1, "Hello there")
end procedure 

-- Call above defined procedure.
sayHello()

This produces the following result −

Hello there

Procedure Parameters

Till now you have seen procedure without a parameter. But there is a facility to pass different parameters while calling a procedure. These passed parameters can be captured inside the procedure and any manipulation can be done over those parameters.

A procedure can take multiple parameters separated by comma.

Example

Let us do a bit modification in our sayHello procedure. This time it takes two parameters −

#!/home/euphoria-4.0b2/bin/eui

procedure sayHello(sequence name,atom  age)
   printf(1, "%s is %d years old.", {name, age})
end procedure

-- Call above defined procedure.
sayHello("zara", 8)

This produces the following result −

zara is 8 years old.

Euphoria - Functions

Euphoria functions are just like procedures, but they return a value, and can be used in an expression. This chapter explains how to write your own functions in Euphoria.

Function Definition

Before we use a function we need to define it. The most common way to define a function in Euphoria is by using the function keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block which ends with end function statement. The basic syntax is shown here −

function functionname(parameter-list)

   statements
   ..........
   return [Euphoria Object]

end function

Example

A simple function called sayHello that takes no parameters is defined here −

function sayHello()
   puts(1, "Hello there")
   return 1
end function

Calling a Function

To invoke a function somewhere later in the script, you would simple need to write the name of that function as follows −

#!/home/euphoria-4.0b2/bin/eui

function sayHello()
   puts(1, "Hello there")
   return 1
end function

-- Call above defined function.
sayHello()

This produces the following result −

Hello there

Function Parameters

Till now we have seen function without a parameters. But there is a facility to pass different parameters while calling a function. These passed parameters can be captured inside the function and any manipulation can be done over those parameters.

A function can take multiple parameters separated by comma.

Example

Let us do a bit modification in our sayHello function. This time it takes two parameters −

#!/home/euphoria-4.0b2/bin/eui

function sayHello(sequence name,atom  age)
   printf(1, "%s is %d years old.", {name, age})
   return 1
end function

-- Call above defined function.
sayHello("zara", 8)

This produces the following result −

zara is 8 years old.

The return Statement

A Euphoria function must have return statement before closing statement end function. Any Euphoria object can be returned. You can, in effect, have multiple return values, by returning a sequence of objects. For example

return {x_pos, y_pos}

If you have nothing to return, then simply return 1 or 0. The return value 1 indicates success and 0 indicates failure

Euphoria - Files I/O

Using Euphoria programming language, you can write programs that read and change file data on your floppy drive or hard drive, or create new files as a form of output. You can even access devices on your computer such as the printer and modem.

This chapter described all the basic I/O functions available in Euphoria. For information on more functions, please refer to standard Euphoria documentation.

Displaying on the Screen

The simplest way to produce output is using the puts() statement where you can pass any string to be displayed on the screen. There is another method printf() which can also be used in case you have to format a string using dynamic values.

These methods convert the expressions you pass them to a string and write the result to standard output as follows −

#!/home/euphoria-4.0b2/bin/eui
 
puts(1, "Euphoria is really a great language, isn't it?" )

This produces the following result on your standard screen −

Euphoria is really a great language, isn't it?

Opening and Closing Files

Euphoria provides basic methods necessary to manipulate files by default. You can do your most of the file manipulation using the following methods −

  • open()
  • close()
  • printf()
  • gets()
  • getc()

The open Method

Before you can read or write a file, you have to open it using Euphoria's built-in open()method. This function creates a file descriptor which is utilized to call other supporting methods associated with it.

Syntax

integer file_num = open(file_name, access_mode)

Above method returns -1 in case there is an error in opening the given file name. Here are the parameters −

  • file_name − The file_name argument is a string value that contains the name of the file that you want to access.

  • access_mode − The access_mode determines the mode in which the file has to be opened. For example, read, write append, etc. A complete list of possible values for file opening modes is given in the following table −

S.No Modes & Description
1

r

Opens a text file for reading only. The file pointer is placed at the beginning of the file.

2

rb

Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file.

3

w

Opens a text file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

4

wb

Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

5

u

Opens a file for both reading and writing. The file pointer is set at the beginning of the file.

6

ub

Opens a file for both reading and writing in binary format. The file pointer is placed at the beginning of the file.

7

a

Opens a file for appending. The file pointer is at the end of the file if the file exists (append mode). If the file does not exist, it creates a new file for writing.

8

ab

Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists (append mode). If the file does not exist, it creates a new file for writing.

Example

The following example creates a new text file in the current directory on your Linux system −

#!/home/euphoria-4.0b2/bin/eui

integer file_num
constant ERROR = 2
constant STDOUT = 1

file_num = open("myfile,txt", "w")

if file_num = -1 then
   puts(ERROR, "couldn't open myfile\n")
else
   puts(STDOUT, "File opend successfully\n")
end if

If file opens successfully, then it "myfile.txt" is created in your current directory and produces the following result −

File opend successfully

The close() Method

The close() method flushes any unwritten information and closes the file, after which no more reading or writing can be done on the file.

Euphoria automatically closes a file when the reference object of a file is reassigned to another file. It is a good practice to use the close() method to close a file.

Syntax

close( file_num );

Here the file descriptor received while opening a file is passed as a parameter.

Example

The following example creates a file as above and then closes it before existing the program −

#!/home/euphoria-4.0b2/bin/eui

integer file_num
constant ERROR = 2
constant STDOUT = 1

file_num = open("myfile.txt", "w")

if file_num = -1 then
   puts(ERROR, "couldn't open myfile\n")
else
   puts(STDOUT, "File opend successfully\n")
end if

if file_num = -1 then
   puts(ERROR, "No need to close the file\n")
else
   close( file_num )
   puts(STDOUT, "File closed successfully\n")
end if

This produces the following result −

File opend successfully
File closed successfully

Reading and Writing Files

Euphoria provides a set of access methods to make our lives easier while reading or writing a file either in text mode or binary mode. Let us see how to use printf() and gets() methods to read and write files.

The printf() Method

The printf() method writes any string to an open file.

Syntax

printf(fn, st, x) 

Here are the parameters −

  • fn − File descriptor received from open() method.

  • st − Format string where decimal or atom is formatted using %d and string or sequence is formatted using %s.

  • x − If x is a sequence, then format specifiers from st are matched with corresponding elements of x. If x is an atom, then normally st contains just one format specifier and it is applied to x. However; if st contains multiple format specifiers, then each one is applied to the same value x.

Example

The following example opens a file and writes the name and age of a person in this file −

#!/home/euphoria-4.0b2/bin/eui

integer file_num
constant ERROR = 2
constant STDOUT = 1

file_num = open("myfile.txt", "w")

if file_num = -1 then
   puts(ERROR, "couldn't open myfile\n")
else
   puts(STDOUT, "File opend successfully\n")
end if

printf(file_num, "My name is %s and age is %d\n", {"Zara", 8})

if file_num = -1 then
   puts(ERROR, "No need to close the file\n")
else
   close( file_num )
   puts(STDOUT, "File closed successfully\n")
end if

The above example creates myfile.txt file. Is writes given content in that file and finally closes. If you open this file, it would have the following content −

My name is Zara and age is 8

The gets() Method

The gets() method reads a string from an open file.

Syntax

gets(file_num)

Here passed parameter is file description return by the opend() method. This method starts reading from the beginning of the file line by line. The characters have values from 0 to 255. The atom -1 is returned on end of file.

Example

Let us take a file myfile.txt which is already created.

#!/home/euphoria-4.0b2/bin/eui

integer file_num
object line

constant ERROR = 2
constant STDOUT = 1

file_num = open("myfile.txt", "r")
if file_num = -1 then
   puts(ERROR, "couldn't open myfile\n")
else
   puts(STDOUT, "File opend successfully\n")
end if

line = gets(file_num)
printf( STDOUT, "Read content : %s\n", {line})

if file_num = -1 then
   puts(ERROR, "No need to close the file\n")
else
   close( file_num )
   puts(STDOUT, "File closed successfully\n")
end if

This produces the following result −

File opend successfully
Read content : My name is Zara and age is 8

File closed successfully

Euphoria provides a list of many methods which helps you in manipulating files. These methods are listed in Euphoria Library Routines.



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