3.8.4 Language Directives

Control the parsing of sections of the scene file:
LANGUAGE_DIRECTIVE:: INCLUDE_DIRECTIVE | IDENTIFIER_DECLARATION | UNDEF_DIRECTIVE | FOPEN_DIRECTIVE | FCLOSE_DIRECTIVE | READ_DIRECTIVE | WRITE_DIRECTIVE | DEFAULT_DIRECTIVE | VERSION_DIRECTIVE | IF_DIRECTIVE | IFDEF_DIRECTIVE | IFNDEF_DIRECTIVE | SWITCH_DIRECTIVE | WHILE_DIRECTIVE | TEXT_STREAM_DIRECTIVE | MACRO_DEFINITION

Insert content of another scene file:
INCLUDE_DIRECTIVE:: #include FILE_NAME; File inclusion may be nested at most 10 levels deep.
FILE_NAME:: STRING

Create an identifier for a value, object, etc.
IDENTIFIER_DECLARATION:: #declare IDENTIFIER = RVALUE [;] | #local IDENTIFIER = RVALUE [;]; Up to 127 characters, starting with a letter, consisting of letters, digits and/or the underscore. The semicolon is required for a FLOAT, VECTOR or COLOR declaration.
RVALUE:: FLOAT | VECTOR | COLOR | USER_FUNCTION | STRING | ARRAY_REFERENCE | SPLINE | TRANSFORM | CAMERA | LIGHT | OBJECT | MATERIAL | INTERIOR | TEXTURE | TEXTURE_MAP | PIGMENT | COLOR_MAP | PIGMENT_MAP | NORMAL | SLOPE_MAP | NORMAL_MAP | FINISH | MEDIA | DENSITY | DENSITY_MAP | FOG | RAINBOW | SKY_SPHERE

Read string, float and/or vector values from a text file:
READ_DIRECTIVE:: #read ( FILE_HANDLE_IDENTIFIER, DATA_IDENTIFIER [, DATA_IDENTIFIER]... ); Use defined(FILE_HANDLE_IDENTIFIER) to detect end-of-file after a read.
DATA_IDENTIFIER:: UNDECLARED_IDENTIFIER | FLOAT_IDENTIFIER | VECTOR_IDENTIFIER | STRING_IDENTIFIER | ARRAY_REFERENCE; May read a value into an array reference if the array element's type has already been established.

Write string, float and/or vector values to a text file:
WRITE_DIRECTIVE:: #write ( FILE_HANDLE_IDENTIFIER, DATA_ITEM [, DATA_ITEM]... )
DATA_ITEM:: FLOAT | VECTOR | STRING

Conditionally parse a section of the scene file, depending on a boolean expression:
IF_DIRECTIVE:: #if ( BOOL ) TOKENS [#else TOKENS] #end
TOKENS:: Any number of POV-Ray keywords, identifiers, values and/or punctuation.

Conditionally parse a section of the scene file, depending on the existence of an identifier:
IFDEF_DIRECTIVE:: #ifdef ( IDENTIFIER ) TOKENS [#else TOKENS] #end
IFNDEF_DIRECTIVE:: #ifndef ( IDENTIFIER ) TOKENS [#else TOKENS] #end

Conditionally parse a section of the scene file, depending on the value of a float expression:
SWITCH_DIRECTIVE:: #switch ( FLOAT ) SWITCH_CLAUSE... [#else TOKENS] #end
SWITCH_CLAUSE:: #case ( FLOAT ) TOKENS [#break] | #range ( F_LOW, F_HIGH ) TOKENS [#break]

Define a macro:
MACRO_DEFINITION:: #macro MACRO_IDENTIFIER ( [PARAM_IDENTIFIER [, PARAM_IDENTIFIER]...] ) TOKENS #end; A parameter identifier may not be repeated in the list.

Invoke a macro:
MACRO_INVOCATION:: MACRO_IDENTIFIER ( [ACTUAL_PARAM [, ACTUAL_PARAM]...] )
ACTUAL_PARAM:

Some directives may be embedded in CAMERA, LIGHT, OBJECT and ATMOSPHERIC_EFFECT statements. However, the directives should only include items (if any) that are valid for a given statement. Also, they should not disrupt the required order of items, where applicable.
EMBEDDED_DIRECTIVE:: IDENTIFIER_DECLARATION | UNDEF_DIRECTIVE | READ_DIRECTIVE | WRITE_DIRECTIVE | IF_DIRECTIVE | IFDEF_DIRECTIVE | IFNDEF_DIRECTIVE | SWITCH_DIRECTIVE | WHILE_DIRECTIVE | TEXT_STREAM_DIRECTIVE