!NULL: A variable of type Undefined.
APP_USER_DIR: Provides access to the application user directory.
APP_USER_DIR_QUERY: Locates existing application user directories.
ARG_PRESENT: Returns TRUE if the value of the specified variable can be passed back to the caller.
BREAKPOINT: Sets and clears breakpoints for debugging.
BYTEORDER: Converts between host and network byte ordering.
CALL_FUNCTION: Calls a function given the function's name as a string.
CALL_METHOD: Calls an IDL object method.
CALL_PROCEDURE: Calls a procedure given the procedure's name as a string.
CATCH: Declares and clears exception handlers.
CODE_COVERAGE: Return line numbers of executed and un-executed code within a routine.
COMMAND_LINE_ARGS: Returns string values supplied when the user starts IDL with the -arg or -args command line options.
CPU: Changes the values stored in the read-only !CPU system variable.
CREATE_STRUCT: Creates and concatenates structures.
COMPILE_OPT: Change default rules for compiling routines.
DEFINE_KEY: Programs keyboard function keys.
DEFINE_MSGBLK: Defines and loads a new message block into the current IDL session.
DEFINE_MSGBLK_FROM_FILE: Reads the definition of a message block from a file, and loads it into the current IDL session.
DEFSYSV: Creates a new system variable.
EXECUTE: Compiles and executes IDL statements contained in a string.
EXIT: Quits IDL and exits back to the operating system.
EXPAND_PATH: Expands path-definition string into full path name for use with the !PATH system variable.
HEAP_FREE: Recursively frees all heap variables referenced by its input argument.
HEAP_GC: Performs garbage collection on heap variables.
HEAP_NOSAVE: Used to clear the save attribute of pointer or object heap variables.
HEAP_REFCOUNT: Returns the current reference count for a pointer or object reference.
HEAP_SAVE: Used to query whether a pointer or object heap variable is savable. It can also be used to change the heap variable save attribute.
IDL_VALIDNAME: Determines whether a string may be used as a valid IDL variable name or structure tag name.
KEYWORD_SET: Returns True if given expression is defined and nonzero or an array.
LAMBDA: Create inline Lambda functions.
LAMBDAP: Create inline Lambda procedures.
LMGR: Determines the type of license used by the current IDL session.
LOGICAL_AND: Performs a logical AND operation on its arguments.
LOGICAL_OR: Performs a logical OR operation on its arguments.
LOGICAL_TRUE: Determines whether its arguments are non-zero (or non-NULL).
MEMORY: Provides information about the amount of dynamic memory currently in use by the IDL session.
MESSAGE: Issues error and informational messages.
N_ELEMENTS: Returns the number of elements contained in an expression or variable.
N_PARAMS: Returns the number of non-keyword parameters used in calling a procedure or function.
N_TAGS: Returns the number of tags in a structure.
OBJ_CLASS: Determines the class name of an object.
OBJ_DESTROY: Destroys an object reference.
OBJ_HASMETHOD: Determines whether an object class implements or inherits a specified method or methods.
OBJ_ISA: Determines inheritance relationship of an object.
OBJ_NEW: Creates an object reference.
OBJ_VALID: Verifies validity of object references.
ON_ERROR: Designates the error recovery method.
ON_IOERROR: Declares I/O error exception handler.
PATH_CACHE: Controls IDL’s path caching mechanism.
PREF_COMMIT: Commits IDL preferences in the pending state.
PREF_GET: Returns information about IDL preferences.
PREF_SET: Sets new values for IDL preferences.
PROFILER: Analyze the performance of IDL code applications.
PTR_FREE: Destroys a pointer.
PTR_NEW: Creates a pointer.
PTR_VALID: Verifies the validity of pointers.
PTRARR: Creates an array of pointers.
RECALL_COMMANDS: Returns entries in IDL’s command recall buffer.
RESOLVE_ALL: Compiles any uncompiled routines.
RESOLVE_ROUTINE: Compiles a routine.
RETALL: Returns control to the main program level.
RETURN: Returns control to the next-higher program level.
ROUTINE_INFO: Provides information about compiled procedures and functions.
STOP: Stops the execution of a running program or batch file.
STRMESSAGE: Returns the text of a given error number.
STRUCT_ASSIGN: Uses relaxed-structure assignment to copy structures.
STRUCT_HIDE: Prevents the IDL HELP procedure from displaying information about structures or objects.
SWAP_ENDIAN: Reverses the byte ordering of scalars, arrays or structures.
SWAP_ENDIAN_INPLACE: Reverses the byte ordering of scalars, arrays or structures, without making a copy.
TAG_NAMES: Returns the names of tags in a structure.
TEMPORARY: Returns a temporary copy of a variable, and sets the original variable to Undefined.
WAIT: Suspends execution of the program for a specified period.