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 (←), e.g. ←A suppresses the display of A.
• Unified index reference, assignment, and modify assignment (R[L], R[L]←A, and R[L]f←A): these three forms all allow both Reach and Scatter indexing — that is, if L⊃R is valid, it is equivalent to ⊃R[⊂L], and if L⌷R is valid, it is equivalent to R[⊃∘.,/L] — Reach and Scatter indexing may appear together within a single instance of R[L], R[L]←A, and R[L]f←A.
• Dyadic operator jot (∘) (composition) is used to join two functions or a function and a variable to produce a derived function (e.g., ,∘⍋∘⍋∘,) which is applied as a single function. For example, the function *∘2 when applied monadically, squares its argument.
• Monadic operator null (⊙): 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 (/⊙)/3 4 instead of (/)/3 4.
• Monadic iota (⍳) extended to negative indices. For example, in origin-0, ⍳¯3 returns ¯3 ¯2 ¯1.
• Monadic iota (⍳) extended to length > 1 vector right arguments returns an array of indices whose shape is that of the right argument (via an internal magic function).
• Dyadic iota (⍳) extended to rank > 1 left arguments returns an array of vector indices to the left argument (via an internal magic function).
• Index reference, assignment, modify assignment, squad, and pick (R[L], R[L]←A, R[L]f←A, L⌷R, and L⊃R) are each extended to negative values in L. That is, if the largest allowed value is N, then the allowable range for the values in L is 1 ¯1[1]-N to N, inclusive. For example, A, A[⍳⍴A], and A[⍳-⍴A] are all identical for any array A in either origin.
• Monadic and dyadic domino (⌹) — matrix inverse/divide extended to use Moore-Penrose pseudo-inverse algorithm via Singular Value Decomposition.
• Prototypes for all primitive functions and operators.
• Out of range numeric assignments to ⎕PP and ⎕PW are set to the value in the allowable range nearest the ceiling of the given number. For example, if ⎕PP is set to 23.7, that value is rounded down to 17, the largest value that system variable may assume.
• Assigning a simple empty vector to a scalar system variable (⎕CT, ⎕IO, ⎕PP, ⎕PW, or ⎕RL) assigns the system default value to the variable.
• New System Variables
  • ⎕FC (Format Control)
  • ⎕IC (Indeterminate Control)
• New System Functions
  • L ⎕CR R (Canonical Representation) — 1=|L (nested vector of character vectors) and 2=|L (character matrix); L<0 returns representations of internal magic functions
  • ⎕DM (Diagnostic Message)
  • ⎕DR R and L ⎕DR R (Data Representation)
  • ⎕ERROR R (Signal Error)
  • ⎕SIZE R (Object Size)
  • ⎕SYSID (System Identification)
  • ⎕SYSVER (System Version)
  • ⎕TC and other related ⎕TCxxx (Terminal Character)
  • L ⎕TF R (Transfer Form) — 1=|L (Type 1 Transfer Form) and 2=|L (Type 2 Transfer Form); L<0 interprets R and the result as Unicode characters; L>0 interprets them as APL2 characters
  • ⎕TYPE R (Object Prototype)
  • ⎕UCS R (Unicode Character Set)
• New Datatypes
  • 2-byte Characters (Unicode, that is, UTF-16)
  • 64-bit Integers
  • APAs (Arithmetic Progression Arrays) (e.g., 2 3 4⍴⍳24)
  • ± Infinity (e.g., ∞ for infinity and ¯∞ for negative infinity) — considerable development work needs to be done to this feature to handle the many special cases

Miscellaneous Syntax

• Strand Assignment: A sequence of names enclosed in parentheses can be assigned to. For example, (A B)←1 2 is the same as A←1 followed by B←2.
• Modify Assignment: An arbitrary (primitive or user-defined) dyadic function may appear immediately to the left of an assignment arrow. For example, Af←1 is the same as A←Af 1, and A[L]f←1 is the same as A[L]←A[L]f 1.
• 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. (A B)f←1 2 is the same as A←Af 1 followed by B←Bf 2).
• Function/operator assignment: A primitive function, operator, or derived function may be assigned to any available name (e.g., F←⍋, or F←¨, or F←∘, or F←+.×).
• 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, (1 2+[1] 2 3⍴R is equivalent to (⍉3 2⍴1 2)+2 3⍴R.
• Axis operator with primitive scalar dyadic functions: The order of the values in the axis operator brackets is significant. For example, (2 3⍴L)+[1 2] 2 3 4⍴R and (⍉2 3⍴L)+[2 1] 2 3 4⍴R are identical.
• 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, (2 3⍴L)⍴¨[1 2] 2 3 4⍴R is equivalent to (3 1 2⍉4⌿1 2 3⍴L)⍴¨2 3 4⍴R.
• 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, ,[2 1] R and ,[1 2] R are both valid and have the same shape and values but, in general, the values are in a different order.
• 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, FOO[2 3] R is valid if the function header is defined as ∇ Z←FOO[X] R.
• Axis operator values may be negative. That is, if the largest allowed value is N, then the allowable range for axis operator values is 1 ¯1[1]-N to N, inclusive.
• 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 ∇ Z←FOO (R₁ R₂ R₃ R₄) 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 ∇ (Z₁ Z₂)←{L₁ L₂ L₃} (LO OP2[X] RO) (R₁ R₂ R₃ R₄).
• Note that braces are required to surround the left argument of an ambivalent function as in ∇ Z←{L} FOO R — Is this an inconsistent extension?
• The result of a user-defined function/operator may be marked as non-displayable by enclosing it in braces, as in ∇ {Z}←FOO R. If the result part of the header consists of multiple names, either ∇ {Z₁ Z₂}←FOO R or ∇ ({Z₁ Z₂})←FOO R or ∇ {(Z₁ Z₂)}←FOO R may be used to mark the result as non-displayable.
• User-defined function/operator prototype line label (⎕PROTOTYPE:): When the user-defined function/operator is called to produce a prototype, this entry point is where execution of the function starts.

System commands

• )CLOSE
• )EDIT
• )EXIT
• )NEWTAB
• )RESET

Session Manager

• Function editor: this feature may be invoked by typing ∇ by itself, or ∇ followed by a name, or )EDIT by itself, or )EDIT followed by a name, or by double-right-clicking on a function name in the session manager or function editor windows
• Multiple workspaces may be open at the same time and switched between via Tabs
• 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
• Multilevel Undo in function editing
• Undo buffer saved with function for reuse on next edit