View source for Consistent Extensions in NARS2000

The following features are considered consistent extensions to the Extended APL Standard in that they replace error-producing behavior with non-error-producing behavior.  Note that Extended APL Standard wants you to know that the use of a consistent extension prevents a program from conforming with the Standard.

== Language Features ==
* [[Sink]]:  monadic left arrow (<apll>←R</apll>) suppresses the display of <apll>R</apll>.
* [[Indexing|Unified index reference, assignment, and modify assignment]] (<apll>R[L]</apll>, <apll>R[L]←A</apll>, and <apll>R[L]<i>f</i>←A</apll>):  these three forms all allow both Reach and Scatter indexing — that is,
** if <apll>L⊃R</apll> is valid, it is equivalent to <apll>⊃R[⊂L]</apll>, and
** if <apll>L⊃¨⊂R</apll> is valid, it is equivalent to <apll>R[L]</apll>, and
** if <apll>L⌷R</apll> is valid, it is equivalent to <apll>R[⊃∘.,/L]</apll>, and
** if <apll>L⌷¨⊂R</apll> is valid, it is equivalent to <apll>⊂¨R[⊂¨L]</apll>
:Reach and Scatter indexing may appear together within a single instance of <apll>R[L]</apll>, <apll>R[L]←A</apll>, and <apll>R[L]<i>f</i>←A</apll>.
* [[Rank|Dyadic operator dieresis-jot]] (<apll><i>f</i>⍤[X] Y</apll>) (rank) is used to apply a function to (monadic) or between (dyadic) cells of the argument(s).
* [[Compose|Dyadic operator jot]] (<apll><i>f</i>∘<i>g</i></apll>) (compose) is used to join two functions or a function and a variable to produce a derived function (e.g., <apll>,∘⍋∘⍋∘,</apll>) which is applied as a single function.  For example, the function <apll>*∘2</apll> when applied monadically, squares its argument.
* [[Null|Monadic operator null]] (<apll><i>f</i>⊙</apll>):  To aid in resolving ambiguities with slash/slope as function/operator, use this operator.  It passes through all functions as functions, and forces the symbols slash/slope to be functions rather than operators.  For example, use <apll>(/⊙)/3 4</apll> instead of <apll>(/)/3 4</apll>.
* [[Partitioned_Enclose|Partitioned Enclose]] (<apll>L⊂[X] R</apll>):  Partition <apll>R</apll> along the <apll>X</apll> axis according to <apll>L</apll>.
* [[Index_Generator|Monadic iota]] (<apll>⍳R</apll>) extended to negative indices.  For example, in origin-0, <apll>⍳¯3</apll> returns <apll>¯3 ¯2 ¯1</apll>.
* [[Index_Generator|Monadic iota]] (<apll>⍳R</apll>) extended to length > 1 vector right arguments returns an array of indices whose shape is that of the right argument.
* [[Index_Of|Dyadic iota]] (<apll>L⍳R</apll>) extended to rank > 1 left arguments returns an array of vector indices to the left argument.
* [[Indexing|Index reference, assignment, modify assignment, squad, transpose, pick, and the axis operator]] (<apll>R[L]</apll>, <apll>R[L]←A</apll>, <apll>R[L]<i>f</i>←A</apll>, <apll>L⌷R</apll>, <apll>L⍉R</apll>, <apll>L⊃R</apll>, and <apll><i>f</i>[L]</apll>) are each extended to negative values in <apll>L</apll>.  That is, if the largest allowed value is <apll>N</apll>, then the allowable range for the values in <apll>L</apll>  is <apll>1 ¯1[1]-N</apll> to <apll>N</apll>, inclusive.  For example, <apll>A</apll>, <apll>A[⍳⍴A]</apll>, and <apll>A[⍳-⍴A]</apll> are all identical for any array <apll>A</apll> in either origin, as are <apll>A</apll>, <apll>(⍳⍴⍴A)⍉A</apll>, and <apll>(⍳-⍴⍴A)⍉A</apll>.
* [[Matrix_Inverse/Divide|Monadic and dyadic domino]] (<apll>⌹R</apll> and <apll>L⌹R</apll>) — matrix inverse/divide extended to use Moore-Penrose pseudo-inverse algorithm via Singular Value Decomposition.
* Prototypes for all primitive functions and operators.
* Jot may be used as either operand to a user-defined operator in which case the name associated with the jot inside the operator is undefined, that is, <apll>⎕NC</apll> on the name returns <apll>0</apll>.
* Generalized Identity Functions for reduction and inner product.
* [[Scalar_System_Variables|Out of range numeric assignments]] to one of these system variables (<apll>⎕CT</apll>, <apll>⎕DT</apll>, <apll>⎕FPC</apll>, <apll>⎕IC</apll>, <apll>⎕IO</apll>, <apll>⎕PP</apll>, <apll>⎕PW</apll>, or <apll>⎕RL</apll>) is set to the value in the allowable range nearest the ceiling of the given number. For example, if <apll>⎕FPC</apll> is set to <apll>23.7</apll>, that value is rounded up to <apll>53</apll>, the smallest value that system variable may assume.
* [[Scalar_System_Variables|Assigning a simple empty vector]] to one of these system variables (<apll>⎕CT</apll>, <apll>⎕DT</apll>, <apll>⎕FPC</apll>, <apll>⎕IC</apll>, <apll>⎕IO</apll>, <apll>⎕PP</apll>, <apll>⎕PW</apll>, or <apll>⎕RL</apll>) assigns the system default value to the variable.
* [[Find]]: dyadic epsilon underbar (<apll>L⍷R</apll>) using the Knuth-Morris-Pratt string searching algorithm.
* [[Reshape]]: (<apll>L⍴R</apll>) is extended to allow a non-empty Reshape of an empty in which case the right argument fill element is used, e.g., <apll>2 3⍴⍬</apll>.
* [[Mismatch]]: Primitive dyadic not equal underbar (<apll>L≢R</apll>) equivalent to <apll>~L≡R</apll>.
* [[Tally]]: Primitive monadic not equal underbar (<apll>≢R</apll>) which is equivalent to <apll>⍬⍴(⍴R),1</apll>.
* [[Indices]]: Primitive monadic iota underbar (<apll>⍸R</apll>) which is equivalent to <apll>(,R)/,⍳⍴1/R</apll>.
* [[Array Lookup]]: Primitive dyadic iota underbar (<apll>L⍸R</apll>) which for matrices looks up the rows of <apll>R</apll> in the rows of <apll>L</apll>.  In general, this function looks up the trailing subarrays of <apll>R</apll> in the vector of trailing subarrays of <apll>L</apll>, and is equivalent to <apll>(⊂⍤¯1 L)⍳⊂⍤(¯1+⍴⍴L) R</apll>.
* [[Type]]: Primitive monadic function down tack (<apll>⊤R</apll>) (Type).
* [[Composition]]: Primitive dyadic operator dieresis circle (<apll>L f⍥g R</apll>) (Composition).
* [[Root]]: Primitive monadic and dyadic functions (<apll>√R</apll> and <apll>L√R</apll>) (Root).
* [[Sets]]:  Primitive dyadic functions (<apll>L§R</apll>, <apll>L⊆R</apll>, and <apll>L⊇R</apll>) (Set functions).
* [[Primes]]: Primitive monadic and dyadic functions pi (<apll>πR</apll> and <apll>LπR</apll>) (Prime decomposition and Number-theoretic functions).
* [[Sequence]]: Primitive dyadic function (<apll>L..R</apll>) (Sequence).
* [[Variant]]:  Primitive dyadic operator quad colon (<apll>f⍠V R</apll> and <apll>L f⍠V R</apll>) (Variant).
* [[Anonymous Functions/Operators]]: one-line grouping of one or more statements all enclosed in braces such as <apll>{(+⌿⍵)÷≢⍵}</apll>.
* [[Determinant]]:  Primitive dyadic operator (<apll>f.g R</apll>) (Determinant Operator).
* [[Convolution]]:  Primitive dyadic operator (<apll>L f⍡g R</apll>) (Convolution Operator).
<!-- * Selective assignment, e.g. <apll>(1 1⍉M)←0</apll>. -->
* New System Variables
** <apll>⎕DT</apll> ([[System_Variable_DT|Distribution Type]])
** <apll>⎕FC</apll> ([[System_Variable_FC|Format Control]])
** <apll>⎕FPC</apll> ([[System_Variable_FPC|Floating Point Control]])
** <apll>⎕IC</apll> ([[System_Variable_IC|Indeterminate Control]])
* New or Changed System Functions
** <apll>⎕A</apll> ([[System_Function_A|Uppercase English Alphabet]]) &mdash; returns the 26-character uppercase English alphabet.
** <apll>⎕AT</apll> ([[System_Function_AT|Object Attributes]]) &mdash; returns various attributes (Valence, Fix Time, Execution Properties, and Size) of an object
** <apll>⎕AV</apll> ([[System_Function_AV|Atomic Vector]]) &mdash; has all UCS-2 Unicode characters (65,536 in length)
** <apll>L ⎕CR R</apll> ([[System_Function_CR|Canonical Representation]]) &mdash; <apll>L=1</apll> (nested vector of character vectors) and <apll>L=2</apll> (character matrix)
** <apll>⎕DM</apll> ([[System_Function_DM|Diagnostic Message]])
** <apll>⎕DR R</apll> and <apll>L ⎕DR R</apll> ([[System_Function_DR|Data Representation]])
** <apll>L ⎕EA R</apll> ([[System_Function_EA|Execute Alternate]])
** <apll>⎕EC R</apll> ([[System_Function_EC|Execute Controlled]])
** <apll>⎕EM</apll> ([[System_Function_EM|Event Message]])
** <apll>⎕ERROR R</apll> ([[System_Function_ERROR|Signal Error]])
** <apll>⎕ES R</apll> and <apll>L ⎕ES R</apll> ([[System_Function_ES|Event Simulate]])
** <apll>⎕ET</apll> ([[System_Function_ET|Event Type]])
** <apll>⎕FMT R</apll> ([[System Function FMT#Monadic_Function|Format arrays within Boxes]])
** <apll>L ⎕FMT R</apll> ([[System Function FMT#Dyadic_Function|Format arrays using Format Phrases]])
** <apll>⎕MF R</apll> ([[System_Function_MF|Monitor Function]])
** <apll>⎕Nxxxx</apll> ([[System_Function_Native_Files|Native File Functions]])
** <apll>⎕NC R</apll> ([[System_Function_NC|Name Class]]) &mdash; returns <apll>21</apll> through <apll>24</apll> for System labels, (Unused), Magic functions, and Magic operators.
** <apll>⎕NL R</apll> ([[System_Function_NL|Name List]]) &mdash; <apll>R=21</apll> through <apll>24</apll> lists System labels, (Unused), Magic functions, and Magic operators.
** <apll>⎕STOP</apll> ([[System_Function_STOP|Query/Set STOP Property On Functions]])
** <apll>⎕SYSID</apll> ([[System_Function_SYSID|System Identification]])
** <apll>⎕SYSVER</apll> ([[System_Function_SYSVER|System Version]])
** <apll>⎕TC</apll> and other related <apll>⎕TC</apll>''xxx'' ([[System_Function_TC|Terminal Control]])
** <apll>L ⎕TF R</apll> ([[System_Function_TF|Transfer Form]]) &mdash; <apll>1=|L</apll> (Type 1 Transfer Form) and <apll>2=|L</apll> (Type 2 Transfer Form); <apll>L&lt;0</apll> interprets <apll>R</apll> and the result as Unicode characters; <apll>L&gt;0</apll> interprets them as APL2 characters
** <apll>⎕TRACE</apll> ([[System_Function_TRACE|Query/Set TRACE Property On Functions]])
** <apll>⎕UCS R</apll> ([[System_Function_UCS|Unicode Character Set]])
** <apll>⎕VR R</apll> ([[System Function VR|Visual Representation]])
** <apll>⎕WA</apll> ([[System Function WA|Workspace Available]])
* New Datatypes
** 2-byte Characters (Unicode, that is, UCS-2)
** 64-bit Integers
** APAs (Arithmetic Progression Arrays) (e.g., <apll>2 3 4⍴⍳24</apll> and <apll>1E12⍴1</apll>)
** ± Infinity (e.g., <apll>∞</apll> for infinity and <apll>¯∞</apll> for negative infinity) — considerable development work needs to be done to this feature to handle the many special cases
** Rational numbers (e.g., <apll>1r3</apll> and <apll>12345x</apll>)
** Variable precision floating point numbers (e.g., <apll>1.234v</apll> and <apll>12v</apll>)

== Miscellaneous Syntax ==
* [[Strand_Assignment|Strand Assignment]]:  A sequence of names enclosed in parentheses can be assigned to.  For example, <apll>(A B)←1 2</apll> is the same as <apll>A←1</apll> followed by <apll>B←2</apll>.
* [[Modify_Assignment|Modify Assignment]]:  An arbitrary (primitive or user-defined) dyadic function may appear immediately to the left of an assignment arrow.  For example, <apll>A<i>f</i>←1</apll> is the same as <apll>A←A<i>f</i> 1</apll>, and <apll>A[L]<i>f</i>←1</apll> is the same as <apll>A[L]←A[L]<i>f</i> 1</apll>.
* [[Modify_Strand_Assignment|Modify Strand Assignment]]:  An arbitrary (primitive or user-defined) dyadic function may appear immediately to the left of the assignment arrow used in Strand Assignment (e.g. <apll>(A B)<i>f</i>←1 2</apll> is the same as <apll>A←A<i>f</i> 1</apll> followed by <apll>B←B<i>f</i> 2</apll>).
* [[Function/Operator_Assignment|Function/operator assignment]]:  A primitive function, operator, or derived function may be assigned to any available name (e.g., <apll>F←⍋</apll>, or <apll>F←¨</apll>, or <apll>F←∘</apll>, or <apll>F←+.×</apll>).
* [[Axis|Axis operator with primitive scalar dyadic functions]]:   The axis operator indicates how the coordinates of the lower rank argument map to the coordinates of the higher rank argument.  For example, <apll>(1 2+[1] 2 3⍴R</apll> is equivalent to <apll>(⍉3 2⍴1 2)+2 3⍴R</apll>.
* [[Axis|Axis operator with primitive scalar dyadic functions]]:  The order of the values in the axis operator brackets is significant.  For example, <apll>(2 3⍴L)+[1 2] 2 3 4⍴R</apll> and <apll>(⍉2 3⍴L)+[2 1] 2 3 4⍴R</apll> are identical.
* [[Axis|Axis operator with the dyadic derived function from the Each operator]]:  As with primitive scalar dyadic functions, the axis operator indicates how the coordinates of the lower rank argument map to the coordinates of the higher rank argument.  For example,  <apll>(2 3⍴L)⍴¨[1 2] 2 3 4⍴R</apll> is equivalent to <apll>(3 1 2⍉4⌿1 2 3⍴L)⍴¨2 3 4⍴R</apll>.
* [[Axis|Axis operator to Ravel]]:  The order of the values in the axis operator brackets is significant, and may transpose coordinates in the right argument before mapping the values to the result.  For example, <apll>,[2 1] R</apll> and <apll>,[1 2] R</apll> are both valid and have the same shape and values but, in general, the values are in a different order.
* [[Axis|Axis operator with user-defined functions/operators]]:  A user-defined function/operator may be sensitive to the axis operator in the same way various primitive functions and operators are.  For example, <apll>FOO[2 3] R</apll> is valid if the function header is defined as <apll>∇ Z←FOO[X] R</apll>.
* [[Axis|Axis operator values may be negative]]:  That is, if the largest allowed value is <apll>N</apll>, then the allowable range for axis operator values is <apll>1 ¯1[1]-N</apll> to <apll>N</apll>, inclusive.
* [[User-Defined_Functions/Operators|Strand left and right arguments and result to user-defined functions/operators]] along with optional left argument may be specified:  For example, a strand right argument may be specified as <apll>∇ Z←FOO (R<sub>1</sub> R<sub>2</sub> R<sub>3</sub> R<sub>4</sub>)</apll> or, more fully, with a non-displayable result and strands used in all of the result, left, and right arguments with an optional left argument may be specified as <apll>∇ (Z<sub>1</sub> Z<sub>2</sub>)←{L<sub>1</sub> L<sub>2</sub> L<sub>3</sub>} (LO OP2[X] RO) (R<sub>1</sub> R<sub>2</sub> R<sub>3</sub> R<sub>4</sub>)</apll>.
* Note that braces are '''required''' to surround the left argument of an ambivalent function as in <apll>∇ Z←{L} FOO R</apll>.
* [[User-Defined_Functions/Operators|The result of a user-defined function/operator]] may be marked as non-displayable by enclosing it in braces, as in <apll>∇ {Z}←FOO R</apll>. If the result part of the header consists of multiple names, either <apll>∇ {Z<sub>1</sub> Z<sub>2</sub>}←FOO R</apll> or <apll>∇ ({Z<sub>1</sub> Z<sub>2</sub>})←FOO R</apll> or <apll>∇ {(Z<sub>1</sub> Z<sub>2</sub>)}←FOO R</apll> may be used to mark the result as non-displayable.
* [[Control_Structures|Control structures]] on one line or split across multiple lines (e.g., <apll>:for I :in ⍳N ⋄ ... ⋄ :endfor</apll>).
* [[Point_Notation|Point Notation]] (<b>Base</b>, <b>Euler</b>, <b>Pi</b>, and <b>Gamma</b>) are extensions to the familiar <b>Decimal</b> and <b>Exponential</b> Point Notation for entering numeric constants.  For example, the numeric constant <apll>16bffff</apll> is a shorthand for calculating <apll>16⊥15 15 15 15</apll>.
* [[Trains]]:  e.g., <apll>avg←(+⌿ ÷ ≢)</apll> applies the functions to its argument(s) in a particular way (in this case, to compute the average of a numeric vector).
* [[System Labels]]:  <apll>⎕PRO</apll>, <apll>⎕ID</apll>, and <apll>⎕MS</apll> in user-defined functions/operators.

== System commands ==
* [[System Command CLOSE|<apll>)CLOSE</apll>]]
* [[System Command COPY|<apll>)COPY</apll>]]
* [[System Command EDIT|<apll>)EDIT</apll>]]
* [[System Command EXIT|<apll>)EXIT</apll>]]
* [[System Command IN|<apll>)IN</apll>]]
* [[System Command INASCII|<apll>)INASCII</apll>]]
* [[System Command NEWTAB|<apll>)NEWTAB</apll>]]
* [[System Command EXIT|<apll>)OFF</apll>]]
* [[System Command OUT|<apll>)OUT</apll>]]
* [[System Command RESET|<apll>)RESET</apll>]]
* [[System Command ULIB|<apll>)ULIB</apll>]]

== Session Manager ==
* [[Function_Editing|Function editor]]:  this feature may be invoked by typing <apll>∇</apll> by itself, or <apll>∇</apll> followed by a name, or <apll>)EDIT</apll> by itself, or <apll>)EDIT</apll> followed by a name, or by double-right-clicking on a function name in the session manager or function editor windows
* [[Session_Manager|Multiple workspaces]] may be open at the same time and switched between via Tabs
* [[Initialization_and_Workspace_Files#Workspace_Files|Workspaces]] are saved as plain text ASCII files
* All variable names are two-byte characters (Unicode, that is, UCS-2)
* Array rank and dimension limit of 64 bits
* [[Session_Manager|Multilevel Undo]] in function editing
* Undo buffer saved with function for reuse on next edit