Pragmatic directives: Difference between revisions
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List any pragmatic directives supported by the language, and demonstrate how to activate and deactivate the pragmatic directives and to describe or demonstrate the scope of effect that the pragmatic directives have within a program.
<br><br>
=={{header|6502 Assembly}}==
These are common to most assemblers but syntax may vary. Place them in your source code file. As with code, all of these can be deactivated by commenting them out.
* <code>org $XXXX</code>: Tells the assembler which memory address to begin assembling at. The instruction after this directive will begin at that address, and then code will be placed sequentially until the end of file or the next ORG directive is reached.
* <code>equ</code>: Equates a label to a specific numeric value. Each instance of that label in your code becomes a constant if preceded by a # and a memory address otherwise.
* <code>include "filename"</code>: Adds an additional file to your source code. The assembler treats the contents as 6502 instructions when assembling. For most assemblers the location of the <code>include</code> statement matters, since it is treated as if the contents were copy-pasted inline.
* <code>incbin "filename"</code>: Adds a binary file to your source code. For most assemblers the location of the <code>incbin</code> statement matters, since it is treated as if the contents were copy-pasted inline.
* <code>ifdef</code>/<code>ifndef</code>/<code>else</code>/<code>endif</code>: The assembler will skip anything inside an IFDEF block if the designated label wasn't defined. IFNDEF and ELSE are the opposite. To make an IFDEF statement true, you only need to have that label defined in your source. (The value doesn't matter as long as it appears.) Here's an example:
<syntaxhighlight lang="6502asm">NMOS_6502 equ 1
ifdef NMOS_6502
txa
pha
else
phx ;NMOS_6502 doesn't have this instruction.
endif ; every ifdef/ifndef needs an endif</syntaxhighlight>
* <code>db</code>/<code>dw</code>/<code>byte</code>/<code>word</code>: Defines a data block. The assembler treats these values as arbitrary bytes rather than machine instructions. Used for tables of values, etc.
* <code>align #</code> Fills in the next # bytes with padding (typically zero, but this value can be adjusted in your assembler's settings. Useful for preventing wasted cycles that occur when crossing a page boundary.
* <code>macro</code>: Defines a macro. Any time the macro name appears in your source document, the assembler replaces it with the definition. Any parameters supplied to the macro are also plugged in. This is useful for parameter passing which would otherwise be very tedious. Every macro must end with an <code>endm</code>.
=={{header|8086 Assembly}}==
These are common to most assemblers but syntax may vary. Place them in your source code file. As with code, all of these can be deactivated by commenting them out.
* <code>.data</code>: Marks the beginning of the data segment. You can load this segment into a segment register with <code>@data</code> rather than <code>seg .data</code>.
* <code>.code</code>: Marks the beginning of the code segment. You can load this segment into a segment register with <code>@code</code> rather than <code>seg .code</code>.
* <code>equ</code>: Equates a label to a specific numeric value.
* <code>include filename</code>: Adds an additional file to your source code. The assembler treats the contents as 6502 instructions when assembling. For most assemblers the location of the <code>include</code> statement matters, since it is treated as if the contents were copy-pasted inline. UASM doesn't require quotation marks around the filename.
* <code>incbin filename</code>: Adds a binary file to your source code. For most assemblers the location of the <code>incbin</code> statement matters, since it is treated as if the contents were copy-pasted inline. UASM doesn't require quotation marks around the filename.
* <code>ifdef</code>/<code>ifndef</code>/<code>else</code>/<code>endif</code>: The assembler will skip anything inside an IFDEF block if the designated label wasn't defined. IFNDEF and ELSE are the opposite. To make an IFDEF statement true, you only need to have that label defined in your source. (The value doesn't matter as long as it appears.)
* <code>db</code>/<code>dw</code>/<code>byte</code>/<code>word</code>: Defines a data block. The assembler treats these values as arbitrary bytes rather than machine instructions. Used for tables of values, etc.
* <code>BYTE n DUP (k)</code>: Fills in the next n bytes with the value k. This is useful for creating user ram in your data segment
* <code>macro</code>: Defines a macro. Any time the macro name appears in your source document, the assembler replaces it with the definition. Any parameters supplied to the macro are also plugged in. This is useful for parameter passing which would otherwise be very tedious. Every macro must end with an <code>endm</code>.
* <code>byte ptr</code>/<code>word ptr</code>: Tells the assembler that the value after this directive is a memory address rather than a constant. This is useful when using labels and the command you're using is somewhat ambiguous about the data size or whether this is an address or a constant.
* <code>seg</code>: When using a labeled code section or memory address as an operand, placing <code>seg</code> in front tells the assembler you wish to load the segment that memory address is located in, rather than the address itself.
* <code>offset</code>: When using a labeled code section or memory address as an operand, placing <code>offset</code> in front tells the assembler you wish to load the offset of that address from the beginning of its segment.
=={{header|Ada}}==
Line 22 ⟶ 69:
* [http://www.adaic.org/resources/add_content/standards/05rm/html/RM-L.html Annex L - Language-Defined Pragmas]
* [http://gcc.gnu.org/onlinedocs/gnat_rm/Implementation-Defined-Pragmas.html GNAT Implementation Defined Pragmas]
=={{header|ALGOL 68}}==
Line 28 ⟶ 74:
{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-2.3.5 algol68g-2.3.5] - most compiler directives are permitted as '''pragma'''s options - also ' '''pr''' read "filename.a68" '''pr''' ' is permitted to "include" a file.}}
{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to implementation specific PRAGMA.}}
'''File: Pragmatic_directives.a68'''<
PRAGMAT portcheck PRAGMAT
Line 39 ⟶ 85:
PROC (REAL)REAL s = sin();
SKIP</
<pre>
10 PROC (REAL)REAL s = sin();
Line 53 ⟶ 99:
{{works with|GWBASIC}}
<
20 TROFF: REM deactivate system trace pragma</
'''
'''
==={{header|IS-BASIC}}===
<syntaxhighlight lang="is-basic">TRACE ON
TRACE OFF</syntaxhighlight>
==={{header|QBasic}}===
<syntaxhighlight lang="qbasic">TRON : REM activate system trace pragma
TROFF : REM deactivate system trace pragma
REM QBasic debugging features make these instructions unnecessary
END</syntaxhighlight>
=={{header|C}}==
The C Preprocessor is well explained on the [https://gcc.gnu.org/onlinedocs/cpp/index.html#Top GNU] site. The pragma page is [https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html here].
<syntaxhighlight lang="c">
/*Almost every C program has the below line,
the #include preprocessor directive is used to
instruct the compiler which files to load before compiling the program.
All preprocessor commands begin with #
*/
#include<stdio.h>
/*The #define preprocessor directive is often used to create abbreviations for code segments*/
#define Hi printf("Hi There.");
/*It can be used, or misused, for rather innovative uses*/
#define start int main(){
#define end return 0;}
start
Hi
/*And here's the nice part, want your compiler to talk to you ?
Just use the #warning pragma if you are using a C99 compliant compiler
like GCC*/
#warning "Don't you have anything better to do ?"
#ifdef __unix__
#warning "What are you doing still working on Unix ?"
printf("\nThis is an Unix system.");
#elif _WIN32
#warning "You couldn't afford a 64 bit ?"
printf("\nThis is a 32 bit Windows system.");
#elif _WIN64
#warning "You couldn't afford an Apple ?"
printf("\nThis is a 64 bit Windows system.");
#endif
end
/*Enlightened ?*/
</syntaxhighlight>
On compilation and output, the compiler type is detected rather than the actual OS :
<pre>
C:\rosettaCode>gcc pragmatic.c
pragmatic.c:22:2: warning: #warning "Don't you have anything better to do ?"
pragmatic.c:28:2: warning: #warning "You couldn't afford a 64 bit ?"
C:\rosettaCode>a
Hi There.
This is a 32 bit Windows system.
</pre>
=={{header|Common Lisp}}==
Line 85 ⟶ 196:
Above would check for the COCOA feature and if not present, load the library. The library is also expected to later push the feature COCOA to the features list. Reading this code then later would ignore the require statement.
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|}}
Delphi has dozens of directive that change the way the compiler and the language work.
Here is a link describing the way directive work in general:
[https://docwiki.embarcadero.com/RADStudio/Alexandria/en/Delphi_compiler_directives Using Delphi Directives]
Here is a list of all the directive available in current versions of Delphi:
https://docwiki.embarcadero.com/RADStudio/Sydney/en/Delphi_Compiler_Directives_(List)_Index
<syntaxhighlight lang="Delphi">
// Some examples
{$R *.dfm}
{$R WorldMaps.res}
{$optimization on,hints off}
{$B+}
{$R- Turn off range checking}
{$I TYPES.INC}
{$M 32768,40960}
{$DEFINE Debug}
{$IFDEF Debug}
{$ENDIF}
procedure DivMod(Dividend: Cardinal; Divisor: Word;
var Result, Remainder: Word);
{$IFDEF PUREPASCAL}
begin
Result := Dividend div Divisor;
Remainder := Dividend mod Divisor;
end;
{$ELSE !PUREPASCAL}
{$IFDEF X86ASM}
asm // StackAlignSafe
PUSH EBX
MOV EBX,EDX
MOV EDX,EAX
SHR EDX,16
DIV BX
MOV EBX,Remainder
MOV [ECX],AX
MOV [EBX],DX
POP EBX
end;
{$ENDIF X86ASM}
{$ENDIF !PUREPASCAL}
</syntaxhighlight>
{{out}}
<pre>
</pre>
=={{header|D}}==
Line 103 ⟶ 277:
More module attributes at [http://www.erlang.org/doc/reference_manual/modules.html].
=={{header|Factor}}==
Factor provides the following compiler declarations which can be used immediately following a word definition:
* '''inline'''
:: Declares the most recently defined word as an inline word. The optimizing compiler copies definitions of inline words when compiling calls to them. Combinators must be inlined in order to compile with the optimizing compiler. For any other word, inlining is merely an optimization.
* '''foldable'''
:: Declares that the most recently defined word may be evaluated at compile-time if all inputs are literal. Foldable words must satisfy a very strong contract:
::* foldable words must not have any observable side effects
::* foldable words must halt — for example, a word computing a series until it coverges should not be foldable, since compilation will not halt in the event the series does not converge
::* both inputs and outputs of foldable words must be immutable
:: Most operations on numbers are foldable. For example, <code>2 2 +</code> compiles to a literal <code>4</code>, since <code>+</code> is declared foldable.
* '''flushable'''
:: Declares that the most recently defined word has no side effects, and thus calls to this word may be pruned by the compiler if the outputs are not used.
:: Note that many words are flushable but not foldable, for example <code>clone</code> and <code><array></code>.
* '''recursive'''
:: Declares the most recently defined word as a recursive word. This declaration is only required for inline words which call themselves.
* '''deprecated'''
:: Declares the most recently defined word as deprecated. Code that uses deprecated words continues to function normally; the errors are purely informational. However, code that uses deprecated words should be updated, for the deprecated words are intended to be removed soon.
Additionally, parsing words sometimes alter compiler behavior. For example, the compiler uses type information from <code>TYPED:</code> words for optimizations.
=={{header|FreeBASIC}}==
FreeBASIC does not have pragmatic directives in the traditional sense.
However, it has several built-in keywords and functions that can affect program behavior in a similar way to pragmatic directives in other languages.
Thus, FreeBASIC has keywords such as <code>Public</code> and <code>Private</code> that can change the visibility of variables and functions within a module.
<syntaxhighlight lang="vbnet">Private Sub i_am_private
End Sub
Public Sub i_am_public
End Sub</syntaxhighlight>
It also has keywords like <code>CDecl</code>, <code>Pascal</code> and <code>StdCall</code> that can change the calling convention of a function.
Cdecl is usually the default calling convention for C compilers and is used almost exclusively on Unix, Linux, *BSD, and DOS-like systems.
<syntaxhighlight lang="vbnet">' declaring 'strcpy' from the standard C library
Declare Function strcpy Cdecl Alias "strcpy" (Byval dest As ZString Ptr, Byval src As ZString Ptr) As ZString Ptr</syntaxhighlight>
Pascal is the default calling convention for procedures in Microsoft QuickBASIC and is the standard convention used in the Windows 3.1 API.
<syntaxhighlight lang="vbnet">Declare Function MyFunctionPascal Pascal Alias "MyFunction" (param As Integer) As Integer</syntaxhighlight>
Stdcall is the default calling convention on Windows and the most common in BASIC languages and the Windows API.
<syntaxhighlight lang="vbnet">Declare Function MyFunc1 Stdcall (param1 As Integer, param2 As Integer) As Integer</syntaxhighlight>
=={{header|Go}}==
Go has a feature called [http://golang.org/pkg/go/build/#overview build constraints] that work on the level of whole files. A comment line reading
<syntaxhighlight lang
will cause the entire file to be excluded from a build unless <expression> is true. The elements, called tags, in the expression are typically things like the target operating system or hardware architecture. For example
<syntaxhighlight lang
will include the file if the target OS is linux, but will exclude the file otherwise. Arbitrary tags can be passed on the command line of the go command. A file could begin
<syntaxhighlight lang
and the build command
<
would only include the file on Tuesdays.
Line 125 ⟶ 350:
=={{header|Icon}} and {{header|Unicon}}==
Icon and Unicon have a number of pragmatic modes. Most of these are controlled via keywords (See [[Special_variables#Icon_and_Unicon]])).
<
&error # controls error handling</
Additionally, tracing can be controlled via the environment variable 'TRACE'.
Line 160 ⟶ 385:
For example,
<syntaxhighlight lang
disables access to the file system (and disables some other features, including the ability to exit the program, because the system exit mechanism is a system feature and thus not trusted). You cannot turn this off after it has been turned on (so you will need to shut down J and start it again if you want to use those features).
Line 166 ⟶ 391:
Or, for example, y is the usual name for the right argument of a verb.
<
8</
But y is also a regular variable. So J also offers a reserved word y. which serves the same role. But this is disabled by default (because mostly it's just an unnecessary complication).
<
|spelling error</
But you can enable the reserved word mechanism:
<
3 :'y.' 8
8
Line 182 ⟶ 407:
8
3 :'y.]y=.7' 8
7</
=={{header|
The closest things which Java has to pragmatic directives are annotations which begin with the @ character.
<syntaxhighlight lang="java">
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public final class PragmaticDirectives {
public static void main(String[] aArgs) {
/* Take no action */
}
@FunctionalInterface
public interface Adder { // This annotation indicates a functional interface,
abstract int add(int a, int b); // which has exactly one abstract method.
}
@Deprecated
public void Display() {
System.out.println("This author is indicating that this method is deprecated");
}
@SuppressWarnings("unchecked")
public void uncheckedWarning() {
List words = new ArrayList();
words.add("hello");
System.out.println("THe compiler is warning that the generic type declaration is missing.");
System.out.println("The correct syntax is: List<String> words = new ArrayList<String>()");
}
@SafeVarargs
public static <T> List<T> list(final T... items) {
System.out.println("This annotation suppresses unchecked warnings about a non-reifiable variable arity type");
return Arrays.asList(items);
}
}
</syntaxhighlight>
=={{header|Julia}}==
Julia has a number of macros which act as compiler directives. For example, the <code>@inbounds</code> macro disables runtime checking of array bounds within a block of code marked by this macro, which sometimes improves performance. Example:
<syntaxhighlight lang="julia">x = rand(100, 100)
y = rand(100, 100)
@inbounds begin
for i = 1:100
for j = 1:100
x[i, j] *= y[i, j]
y[i, j] += x[i, j]
end
end
end
</syntaxhighlight>
=={{header|Kotlin}}==
The closest things which Kotlin has to pragmatic directives are annotations which always begin with the @ character. For example, the following code would normally produce a compiler warning that the variable 's' is never used. However, the presence of the @Suppress annotation suppresses the warning:
<syntaxhighlight lang="scala">// version 1.0.6
@Suppress("UNUSED_VARIABLE")
fun main(args: Array<String>) {
val s = "To be suppressed"
}</syntaxhighlight>
=={{header|Lua}}==
Lua itself really doesn't have anything equivalent. However, if being used in a mixed/hosted/embedded environment, the <code>ffi</code> library might be encountered, which supports <code>pragma pack</code> to facilitate native type interchange:
<syntaxhighlight lang="lua">ffi = require("ffi")
ffi.cdef[[
#pragma pack(1)
typedef struct { char c; int i; } foo;
#pragma pack(4)
typedef struct { char c; int i; } bar;
]]
print(ffi.sizeof(ffi.new("foo")))
print(ffi.sizeof(ffi.new("bar")))</syntaxhighlight>
{{out}}
<pre>5
8</pre>
=={{header|Mathematica}}/{{header|Wolfram Language}}==
Mathematica makes no formal difference between any normal and "specific" operation of the language.
Any possible desired effect can be achieved by calling a function or setting a variable.
Line 193 ⟶ 497:
NetRexx provides three pragma-like instructions: <tt>OPTIONS</tt>, <tt>NUMERIC</tt> and <tt>TRACE</tt>.
* '''<tt>OPTIONS</tt>''' provides the ability to pass special requests to the language processor (i.e. a compiler or interpreter).
:The syntax is:<syntaxhighlight lang
:where ''wordlist'' is one or more symbols separated by blanks. The individual words in ''wordlist'' might control optimizations, enforce standards, enable implementation-dependent features, etc.
:The current default settings of <tt>OPTIONS</tt> is:<
nobinary nocomments nocompact console crossref decimal nodiag noexplicit noformat java logo noreplace nosavelog nosourcedir -
nostrictargs nostrictassign nostrictcase nostrictimport nostrictprops nostrictsignal nosymbols trace2 noutf8 verbose3</
* '''<tt>NUMERIC</tt>''' is used to change the way in which arithmetic operations are carried out by a program.
:The syntax is:<
numeric form [scientific | engineering];</
:*'''<tt>numeric digits</tt>''' controls the precision under which arithmetic operations will be evaluated. The default for ''exprd'' is '''9''' i.e. '''<tt>numeric digits 9</tt>'''.<br />There is normally no limit to the value for <tt>'''numeric digits'''</tt> (except the constraints imposed by the amount of storage and other resources available) but note that high precisions are likely to be expensive in processing time.
:*'''<tt>numeric form</tt>''' controls which form of exponential notation is to be used for the results of operations.
* '''<tt>TRACE</tt>''' is used to control the tracing of the execution of NetRexx methods, and is primarily used for debugging.
:The Syntax is:<
trace var [varlist]</
:where ''tracesetting'' is one of:
:*'''<tt>all</tt>'''
Line 216 ⟶ 520:
::similar to <tt>trace all</tt> for the clauses in a <tt>method</tt> with the addition that the results of all ''expression'' evaluations and any results assigned to a variable by an assignment, <tt>loop</tt>, or <tt>parse</tt> instruction are also traced.
:and ''varlist'' provides a list of variables which will be monitored during execution.
=={{header|Nim}}==
Nim provides a great number of directives known as pragmas. It is not possible to describe them here. A pragma (or list of pragmas) starts with <code>{.</code> and ends with <code>.}</code>. It may possess arguments. Here are some kinds of pragmas:
:– pragmas such as <code>pure</code> applicable to types;
:– pragmas such as <code>noSideEffect</code>, <code>compileTime</code> applicable to procedures;
:– compilation option pragmas, especially to disable or enable runtime checks;
:– <code>push</code> and <code>pop</code> pragmas to deactivate/reactivate options;
:– pragmas for objects, such as <code>inheritable</code> or <code>final</code>;
:– pragmas such as <code>linearScanEnd</code> or <code>computedGoto</code> which change the way the code is generated;
:– pragmas for variables such as <code>register</code> or <code>global</code>;
:– pragmas such as <code>hint</code> to make the compiler output a message at compilation;
:– pragmas such as <code>used</code> to avoid a warning message (here when a variable is not used);
:– <code>experimental</code> pragma to activate experimental features;
:– <code>deprecated</code> pragma to mark a type, procedure, etc. as deprecated with emission of a warning at compile time;
:– pragmas to interface with other languages: <code>importc</code>, <code>extern</code>, <code>bycopy</code>, <code>byref</code>, <code>varargs</code>, etc.
:– pragmas to declare the calling convention of a procedure: <code>nimcall</code>, <code>closure</code>, <code>stdcall</code>, <code>cdecl</code>, <code>inline</code>, etc.
:– implementation specific pragmas: <code>bitsize</code>, <code>align</code>, <code>volatile</code>, etc.
:- pragmas for templates such as <code>inject</code>, <code>gensym</code>;
:– thread pragmas;
:– pragma <code>pragma</code> which allows the users to define their own pragmas.
And here are some examples:
<syntaxhighlight lang="nim">{.checks: off, optimization: speed.} # Checks are deactivated and code is generated for speed.
# Define a type Color as pure which implies that value names are declared in their own scope
# and may/should be accessed with their type qualifier (as Color.Red).
type Color {.pure.} = enum Red, Green, Blue
# Declare a procedure to inline if possible.
proc odd(x: int): bool {.inline.} = (x and 1) != 0
# Declaration of a C external procedure.
proc printf(formatstr: cstring) {.header: "<stdio.h>", importc: "printf", varargs.}
# Declaration of a deprecated procedure. If not used, no warning will be emitted.
proc notUsed(x: int) {.used, deprecated.} = echo x
# Declaration of a type with an alignment constraint.
type SseType = object
sseData {.align(16).}: array[4, float32]
# Declaration of a procedure containing a variable to store in register, if possible, and a variable to store as global.
proc p() =
var x {.register.}: int
var y {.global.} = "abcdef"
{.push checks: on.}
# From here, checks are activated.
...
{.pop.}
# From here, checks are deactivated again.</syntaxhighlight>
=={{header|Perl}}==
Line 238 ⟶ 593:
Pragmatic modules have local scope and are utilized using the use directive:
<
use strict; # use strict pragma module</
To disable behaviour of a pragmatic module:
<
no strict; # disable strict pragma module</
=={{header|Phix}}==
The following are taken directly from the Phix.syn (syntax colouring) file, which can be edited as needed (for errors or new compiler features): <br>
Delimiters #$:.%\^ <br>
Operators , = := == != < <= >
Braces 7 ()[]{} <br>
BlockComment /* */ --/* --*/ #[ #] <br>
LineComment -- // <br>
TokenStart abcedfghijklmnopqrstuvwxyz <br>
TokenStart ABCDEFGHIJKLMNOPQRSTUVWXYZ_ <br>
Line 268 ⟶ 615:
The last line means that escapes in string literals start with a backslash, and there are 14 of them: CR, LF,
TAB, backslash, single and double quotes, escape (#1B, e and E allowed), hex byte (# and x allowed), NUL,
backspace, and 4 and 8-digit unicode characters. The 7 in Braces is just the number of nested colours to use.
(The above is further explained on [[[[Special_characters#Phix|Special_characters]]]])
Line 276 ⟶ 623:
The #ilASM{} directive contains inline assembly, which can contain PE/ELF/32/64 guards to control the exact
code emitted,
day I hope/expect to add a JS guard, for pwa/p2js, but there isn't one yet.
The #isginfo{}, #isinit{}, and #istype{} directives instruct the compiler to perform various type-inference
Line 283 ⟶ 631:
The with/without directives control several run-time options: <br>
javascript -- ensure pwa/p2js compatible, ie can be run in a browser, equivalent to js and javascript_semantics<br>
profile -- produce an execution count listing when the program terminates<br>
profile_time -- produce an execution percentage listing when the program terminates<br>
safe_mode -- see [[[[Untrusted_environment#Phix]]]]<br>
type_check -- turn user-defined type checking on or off (can make it noticeably faster, once testing is done)<br>
trace -- allow or disallow debugging (source code line-by-line tracing) <br>
debug -- turn debugging info generation on or off <br>
nested_globals -- fine-grained scope control, nested_locals is the complementary option <br>
The last two are related: without debug completely removes all tracing and diagnostics for a specific file (primarily intended for use in well-tested system routines), whereas (under with debug, which is the default) with/without trace can make debugging less tedious by not stopping on every line of irrelevant (user-selected) code, although dumps still contain a full call stack. Some other options, specifically indirect_includes, inline, and digital stamps, exist solely for compatability and are completely ignored.
with/without console/gui still work but should now be replaced with a format directive:
format PE32|PE64|ELF32|ELF64 - you can also specify gui/console, subsystem version, icons and manifest files. Ignored when interpreting/transpiling.
The following are ignored by the compiler, but are respected by the source code reindent tool: <br>
Line 301 ⟶ 652:
--#withtype <br>
While technically code rather than a directive, the requires() builtin can hopefully avoid fruitless efforts to run something where it is simply never going to work, eg
<!--<syntaxhighlight lang="phix">(phixonline)-->
<span style="color: #7060A8;">requires</span><span style="color: #0000FF;">(</span><span style="color: #004600;">JS</span><span style="color: #0000FF;">)</span>
<span style="color: #000080;font-style:italic;">--requires(WINDOWS) -- (one of only, or
--requires(LINUX) -- a special combo)</span>
<span style="color: #7060A8;">requires</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"1.0.2"</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">requires</span><span style="color: #0000FF;">(</span><span style="color: #000000;">32</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">-- or 64</span>
<!--</syntaxhighlight>-->
=={{header|PicoLisp}}==
Line 318 ⟶ 678:
an array.
For example:
<
i=101;
t(i)=0;</
will cause unpredictible results.
And :
<
declare (t(100),i) fixed binary;
i=101;
t(i)=0;
end;</
will issue the message : "The SubscriptRange condition was raised." at execution time.
<br>Or, it can be handle by an on-unit.
<
declare (t(100),i) fixed binary;
i=101;
Line 336 ⟶ 696:
t(i)=0;
e:on SubscriptRange system; /* default dehaviour */
end;</
<br>And the same way for a string,
the '''StringRange''' condition is raised when a substring reference is beyond
Line 345 ⟶ 705:
<br>The '''Size''' condition is raised when a numerical value is shorten
as a result of a convertion assigment.
=={{header|PowerShell}}==
The #Requires statement prevents a script from running unless the Windows
PowerShell version, modules, snap-ins, and module and snap-in version
prerequisites are met. If the prerequisites are not met, Windows PowerShell
does not run the script.
You can use #Requires statements in any script. You cannot use them in
functions, cmdlets, or snap-ins.
<syntaxhighlight lang="powershell">
#Requires -Version <N>[.<n>]
#Requires –PSSnapin <PSSnapin-Name> [-Version <N>[.<n>]]
#Requires -Modules { <Module-Name> | <Hashtable> }
#Requires –ShellId <ShellId>
#Requires -RunAsAdministrator
</syntaxhighlight>
For a full description:
<syntaxhighlight lang="powershell">
Get-Help about_Requires
</syntaxhighlight>
=={{header|PureBasic}}==
PureBasic supports several pragmatic directives, also known as '''[https://www.purebasic.com/documentation/reference/compilerdirectives.html compiler directives]'''.
<code>CompilerIf…CompilerElseIf…CompilerElse…CompilerEndIf</code>: allows certain parts of the code to be compiled depending on the evaluation of a constant expression.
<syntaxhighlight lang="vb">CompilerIf #PB_Compiler_OS = #PB_OS_Linux
; some Linux specific code
CompilerElse
; some code for other operating systems
CompilerEndIf</syntaxhighlight>
<code>CompilerSelect…CompilerCase…CompilerDefault…CompilerEndSelect</code>: Allows you to select which code to compile based on a constant numeric value.
<syntaxhighlight lang="vb">CompilerSelect #PB_Compiler_OS
CompilerCase #PB_OS_MacOS
; some Mac OS
CompilerCase #PB_OS_Linux
; some Linux specific code
CompilerEndSelect</syntaxhighlight>
<code>CompilerError</code> and <code>CompilerWarning</code>: generate an error or a warning, respectively.
<syntaxhighlight lang="vb">CompilerIf #PB_Compiler_OS = #PB_OS_Linux
CompilerError "Linux is not supported, sorry."
CompilerElse
CompilerWarning "OS supported, you can now comment me."
CompilerEndIf</syntaxhighlight>
<code>EnableExplicit</code> and <code>DisableExplicit1</code>: Enable or disable explicit mode. When enabled, all variables not explicitly declared with Define, Global, Protected, or Static will not be accepted and the compiler will generate an error.
<syntaxhighlight lang="vb">EnableExplicit
Defines
a = 20 ; Ok, as declared with 'Define'
b = 10 ; Will raise an error here</syntaxhighlight>
<code>EnableASM</code> and <code>DisableASM</code>: Enable or disable the inline assembler. When enabled, all assembler keywords are available directly in the source code.
<syntaxhighlight lang="vb">; x86 assembly example
Test = 10
EnableASM
MOV dword [v_Test],20
DisableASM
DebugTest ; Will be 20</syntaxhighlight>
It is important to note that the scope of these directives is global, that is, they affect all code after them until a directive is found that disables them or until the end of the code file.
=={{header|Python}}==
Line 350 ⟶ 771:
;Python 3.2:
<
Type "copyright", "credits" or "license()" for more information.
>>> import __future__
>>> __future__.all_feature_names
['nested_scopes', 'generators', 'division', 'absolute_import', 'with_statement', 'print_function', 'unicode_literals', 'barry_as_FLUFL']
>>> </
('barry_as_FLUFL' is an April fools [http://www.python.org/dev/peps/pep-0401/ joke])
;Python 2.7:
<
Type "copyright", "credits" or "license()" for more information.
>>> import __future__
>>> __future__.all_feature_names
['nested_scopes', 'generators', 'division', 'absolute_import', 'with_statement', 'print_function', 'unicode_literals']
>>> </
=={{header|Racket}}==
Racket eschews pragmas that are specified outside of the language. However, one can view Racket's <tt>#lang</tt> mechanism as a much more powerful tool for achieving similar things. For example, normal code starts with <tt>#lang racket</tt> -- giving you a very Scheme-like language; change it to <tt>#lang typed/racket</tt> and you get a similar language that is statically typed; use <tt>#lang lazy</tt> and you get a Racket-like language that has lazy semantics; use <tt>#lang algol60</tt> and you get something that is very different than Racket. (And of course, you can implement your own language quite easily.)
=={{header|Raku}}==
(formerly Perl 6)
{{works with|rakudo|2015-10-20}}
The Perl 6 pragma mechanism is nearly identical to Perl 5's, piggybacking on the notation for importing modules (pragmas are distinguished by case from normal modules, which are generally of mixed case). By convention pragmas are lowercase, unless they are indicating the use of an unsafe feature, in which case they are in all caps.
<syntaxhighlight lang="raku" line>use MONKEY-TYPING;
augment class Int {
method times (&what) { what() xx self } # pretend like we're Ruby
}</syntaxhighlight>
Unlike Perl 5, there is no <tt>use strict;</tt> pragma, however, since Perl 6 is strict by default. Importation of a pragma is lexically scoped as in Perl 5, but note that unlike in Perl 5, <i>all</i> importation is lexical in Perl 6, so pragmas are not special that way.
=={{header|REXX}}==
Line 535 ⟶ 966:
For external routines, the defaults are used. <br><br>
=={{header|RPL}}==
Pragmatic directives are given through system flags that can bet with the <code>SF</code> and <code>CF</code> commands anywhere in a program.
System flags are a legacy of programmable calculators and unfortunately, which flag to set or reset for a specific directive depends on the calculator model you are using.
As an example, here are the directives controlled by flags on HP-28 models:
* LAST variable activated
* Immediate evaluation of constants (e, pi...) and functions
* length of binary words
* display and print formats
* decimal sign and object separator
* real number display format
* sound on/off
* underflow/overflow error handling
Fortunately, some of them can also be operated through language commands, such as <code>STWS</code> (defines the length of binary words) or <code>RAD</code> (defines radian as the trigonometric unit).
=={{header|Scala}}==
===tailrec===
<syntaxhighlight lang="scala">@inline
@tailrec</syntaxhighlight>
=={{header|Tcl}}==
Line 561 ⟶ 1,013:
Pragmatic directives remain effective, until they are deactivated, or the end of the script is reached:
<
set +vx # Deactivate both pragmatic directives</
=={{header|Wren}}==
The closest thing Wren has to a pragmatic directive is its '''import''' statement which loads a module, executes its source code and imports variable names from that module into the current scope.
Import statements can appear anywhere a variable declaration is allowed and in particular within conditional structures. This enables us to do things such as the following:
<syntaxhighlight lang="wren">/* windows.wren */
class Windows {
static message { "Using Windows" }
static lineSeparator { "\\r\\n" }
}</syntaxhighlight>
<syntaxhighlight lang="wren">/* linux.wren */
class Linux {
static message { "Using Linux" }
static lineSeparator { "\\n" }
}</syntaxhighlight>
<syntaxhighlight lang="wren">/* Pragmatic_directives.wren */
import "os" for Platform
var os
if (Platform.isWindows) {
import "./windows" for Windows
os = Windows
} else {
import "./linux" for Linux
os = Linux
}
System.print("%(os.message) which has a \"%(os.lineSeparator)\" line separator.")</syntaxhighlight>
{{out}}
From the last script, when run on a Linux system.
<pre>
$ wren_cli Pragmatic_directives.wren
Using Linux which has a "\n" line separator.
</pre>
=={{header|XPL0}}==
XPL0 has a single compiler directive called "string." It changes the way
text strings are terminated.
Originally, strings were terminated by setting the most significant bit set on
the last character. This conserved memory on early personal computers
such as the Apple II by making strings one byte shorter than if they were
terminated by a zero byte. As computer memory grew, this method became
less desirable. It prevented using the extended character codes 128
through 255 in strings, and it prevented null strings ("").
The RawText intrinsic was added as an alternative to the Text intrinsic
that enabled extended characters to be displayed in strings. It relied on
a final space character added by the programmer that had its high bit set
($A0) and was not displayed.
To make XPL0 more consistent with programming standards, in 2012 the
"string" directive was added.
string 0; \makes all following strings in the code zero-terminated
string 1; \(or any non-zero argument) reverts to MSB termination
{{omit from|AWK}}
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