# Introduction

This chapter covers the system services available in the standard system module.

## Interpreter information

The interpreter provides a set reserved names that are related to the system platform. Example 0501.als demonstrates the available information.

zsh> axi 0501.als program name : afnix operating system name : linux operating system type : unix afnix official uri : http://www.afnix.org

### Interpreter version

The interpreter version is identified by 3 numbers called major, minor and patch numbers. A change in the major number represents a major change in the writing system. The minor number indicates a major change in the interface or libraries. A change in the patch number indicates bug fixes. All values are accessed via the interpreter itself. The `major-version`, `minor-version`, `patch-version` symbols are bound to these values.

println "major version number : " interp:major-version println "minor version number : " interp:minor-version println "patch version number : " interp:patch-version

### Operating system

The operating system is uniquely identified by its name. The operating system type (or category) uniquely identifies the operating system flavor.

println "operating system name : " interp:os-name println "operating system type : " interp:os-type

### Program information

Program information are carried by two symbols that identifies the program name and the official uri. While the first might be useful, the second one is mostly used by demo programs.

println "program name : " interp:program-name println "afnix official uri : " interp:afnix-uri

## System services

The system services module provides various functions that cannot be classified into any particular category.

### System services functions

Function | Description
--- | ---
exit | terminate with an exit code
sleep | pause for a certain time
get-pid | get the process identifier
get-env | get an environment variable
get-host-name | get the host name
get-user-name | get the user name

The `exit` function terminates the program with an exit code specified as the argument. The `sleep` function pause the specific thread for a certain time. The time argument is expressed in milliseconds. The `get-pid` function returns the process identifier. The `get-env` function returns the environment variable associated with the string argument. The `get-host-name` function returns the host name. The host name can be either a simple name or a canonical name with its domain, depending on the system configuration. The `get-user-name` function returns the current user name.

## Time and date

The `Time` and `Date` classes are classes designed to manipulate time and date. The writing system operates with a special coordinated time which uses the reference of Jan 1st 0000 in a modified proleptic Gregorian calendar. This proleptic feature means that the actual calendar (Gregorian) is extended beyond year 1582 (its introduction year) and modified in order to support the year 0. This kind of calendar is somehow similar to the astronomical Gregorian calendar except that the reference date is 0 for the writing system. This method presents the advantage to support negative time. It should be noted that the 0 reference does not means year 1BC since year 0 did not exist at that time (the concept of zero is fairly new) and more important, the date expressed in the form 1BC generally refers to the Julian calendar since the date is before 1582. Although, the class provides several methods to access the time and date fields, it is also possible to get a string representation that conforms to ISO-8601 or to RFC-2822.

### Time and date construction

By default, a time instance of current time is constructed. This time reference is obtained form the machine time and adjusted for the internal representation. One feature of this class is that the time instance does not have to be bounded with 24 hours. The time stored is the absolute time, which should be considered like a temporal reference -- or date -- those origin is 0 in some calendar representation.

const time (afnix:sys:Time) assert true (afnxi:sys:time-p time)

A simple time representation can also be built by hours, minutes and seconds. In this case, the time is a time definition at day 0 in the reference calendar.

const time (afnix:sys:Time 12 23 54)

By default a date instance of the current date is constructed. The current date is computed from the machine time and expressed in a particular calendar. By default, the engine uses a special Gregorian calendar as explained before. The important point here s that the date will show up like the user should expect.

const date (afnix:sys:Date) assert true (afnix:sys:date-p date)

A date instance can also be built with an absolute time expressed in seconds or with specific elements. with one argument, the date is expressed in seconds since the origin. Since the internal representation is 64 bits, the date room is quite large. For example, the absolute time to represent Jan 1st 1970 is 62167219200 seconds. This epoch is used to adjust the system time on some UNIX system. Another way to create a specific date is to use the date descriptor by year, month and day. With 6 arguments, the time components can also be given. This makes `Date` one of the constructor that accept the largest number of arguments.

const date (afnix:sys:Date 1789 7 14 16 0 0) assert true (afnix:sys:date-p date)

In the previous example, at 17:00 local time, 16:00Z although the concept of time zone was not formalized, the Bastille surrenders on July 14 1789. This example shows that extreme care should be used when dealing with old dates. Note that a simpler form could have been used to set that date. With 3 argument, the date is set at time 00:00:00Z.

const date (afnix:sys:Date 1789 7 14) assert true (afnix:sys:date-p date)

### Time and date representation

Except for some special applications -- like the cookie maximum age --, the date representation is quite standard and can be found either in the form of ISO-8601 or RFC-2822.

const time (afnix:sys:Time 12 44 55) println (time:format) # 12:44:55 println (time:to-iso) # 14:44:55 println (time:to-rfc) # 14:44:55 +0200

in the first form, the time is represented naturally by hour, minutes and seconds. By default, it is the local time that is given. With a flag set to true, the UTC time is displayed. In the second form, the time is displayed in the ISO-8601 form which is the same as before. In the third form, the time is displayed in the RFC-2822 form. This form is always expressed locally with the timezone difference associated with it. It shall be noted that the ISO-8601 mandate to use the suffix 'Z' for the zulu time. This is the difference when using the `true` flag with the `format` and `to-iso` methods.

println (time:format true) # 12:44:55 println (time:to-iso true) # 12:44:55Z

The date representation also operates with 3 methods, namely `format`, `to-iso` and `to-rfc`. For example, if the time is 12:00 in Paris on July 14th 2000, the date will be displayed like below.

const date (afnix:sys:Date 2000 7 14 12 0 0) println (date:format) # Fri Jul 14 07:00:00 2000 println (date:to-iso) # 2000-07-14T07:00:00 println (date:to-rfc) # Fri, 14 Jul 2000 07:00:00 -0500

The example show the local time. With UTC display, only the first two methods can be used.

const date (afnix:sys:Date 2000 7 14 12 0 0) println (date:format true) # Fri Jul 14 12:00:00 2000 println (date:to-iso true) # 2000-07-14T12:00:00Z

## Options parsing

The `Options` class provides a convenient mechanism to define a set of options and to parse them in a simple way. The object is constructed by specifying which option is valid and how it behaves. The arguments can be passed to the object for subsequent analysis. An option can be either a unique option or a string option. In this later case, multiple value for the same option can be accepted. In that case, the option is said to be a string vector option. An option can be also an option list. I that case, the option is defined with a set of valid string. A list option is associated with a boolean flag for each string defined with that option.

### Option creation

An `Options` is created by invoking the constructor with or without a user message. The user message is used by the `usage` method which display an information message.

const options (afnix:sys:Options "axi [options] [file [arguments]]")

Eventually, the `set-user-message` method can be used to set the user message.

### Options definition

The process of defining options is done by specifying the option character, eventually an option string and an option message.

options:add-unique-option 'h' "print this help message" options:add-unique-option 'v' "print system version" options:add-vector-option 'i' "add a resolver path" options:add-string-option 'e' "force the encoding mode" options:add-list-option 'f' "assert" "enable assertion checks" options:add-list-option 'f' "nopath" "do not set initial path"

The above example shows the option descriptors for the interpreter. Since `i` is a vector option, multiple occurrences of that option is allowed. It shall be noted that the list option `f assert` is a debug option. This means that this option is always set when the program is compiled in debug mode.

### Options parsing and retrieval

A string vector is parsed with the `parse` method. Generally, the vector argument is the interpreter argument vector defined in the qualified name `interp:args`. When the vector has been successfully parsed, it is possible to check the option that have been set.

options:parse (Vector "-h") if (options:get-unique-option 'h') { options:usage afnix:sys:exit 0 }

In the above example, the option vector is parsed with the `parse` method. The `get-unique-option` method returns true for the `h` thus triggering the display of the usage message.

usage: axi [options] [file [arguments]] [h] print this help message [v] print system version [i path] add a resolver path [e mode] force the encoding mode [f assert] enable assertion checks [f nopath] do not set initial path

If the option is a string option, the `get-string-option` will return the string associated with that option. It shall be noted that the `get-unique-option` method can be used to check if the option has been set during the parsing process. If the option is a vector option, the `get-vector-option` method is more appropriate. In this case, a vector is returned with all strings matching this option.

options:parse (Vector "-i" "../" "-i" "../.." -e "UTF-08" "hello")

In the previous example, the vector option `i` is set two times. The associated vector option has therefore a length of 2. The string option `e` is set to UTF-08. For this option `e`, the `get-unique-option` method will return true. Finally, the vector argument is filled with one string argument.