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 ←, e.g. ←A to suppress 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., f←,∘⍋∘⍋∘,) which is applied as a single function. For example, the function f←*∘2 when applied monadically, squares its argument.

• Miscellaneous Syntax
  • Strand Assignment: A sequence of names enclosed in parentheses can be assigned to, e.g. (A B)←1 2 is the same as A←1 and B←2.
  • Modify Assignment: An arbitrary (primitive or user-defined) dyadic function may appear immediately to the left of an assignment arrow, e.g. 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 and 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←∘).
  • 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 may transpose coordinates: 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 2 3⍴L)⍴¨2 3 4⍴R (assuming L has only six elements).
  • Axis operator to Ravel may transpose coordinates (e.g., ,[2 1] R and ,[1 2] R are both valid but, in general, have the same values in different order).

• 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.