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:

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]fn←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]fn←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).
• ± 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.
• 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.
• System variables
  • ⎕FC (Format Control)
  • ⎕IC (Indeterminate Control)
• System functions
  • 1 ⎕CR R (Canonical Representation -- vector result) and 2 ⎕CR R (matrix result)
  • ⎕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)
  • ⎕TYPE R (Object Prototype)
  • ⎕UCS R (Unicode Character Set)

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, A fn←1 is the same as A←A fn 1, and A[L]fn←1 is the same as A[L]←A[L] fn 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)fn←1 2 is the same as A←A fn 1 followed by B←B fn 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 (3 2⍴L)+[2 1] 2 3 4⍴R are both valid but, in general, have different values.
• 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 as are various primitive functions and operators. For example, foo[2 3] R is valid if the function header is defined as ∇ Z←foo[X] R.
• Except for where fractional values are allowed (laminate and certain cases of ravel), 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-N to N, inclusive.
• Strand left and right arguments and result to user-defined functions/operators along with optional left argument (e.g., ∇ Z←FOO (R1 R2 R3 R4) or, more fully, ∇ (Z1 Z2)←[L1 L2 L3] (LO OP2[X] RO) (R1 R2 R3 R4).
• Note that brackets are required to surround the left argument of an ambivalent function as in ∇ Z←[L] FOO R — Is this an inconsistent extension?
• 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.