Stop

Stop (⊣) (in SHARP APL and APLX), Hide (in GNU APL and Kap), or Null (in A+) is a primitive monadic function that ignores its argument and returns a non-printing value. It shares the left tack glyph with Left Identity. The nature of the returned value can vary: for example an empty matrix is used in SAX and APLX, while GNU APL uses the scalar 0 but returns it as a shy result (or "committed"). In SHARP APL's initial implementation of ⊣, Stop returned "no result", so that attempting to use its result would be an error.^[1]

In other dialects, monadic ⊣ is the identity function, exactly like ⊢. This redundancy means that it can be redefined without losing any primitive functionality. However, pairing both dyadic functions with the identity may be useful in constructing ambivalent functions, particularly in tacit programming. In April, monadic ⊣ ("Empty") returns its argument is returned as a shy result, giving it the properties of both Stop and the identity.

In dialects where ⊣ does not return the argument when used monadically, the effect can be achieved with ⊢⍨ using the commute operator.

Documentation

APLX
Kap

References

↑ "Language Extensions of May 1983". SATN-45, 1983-05-02.

APL built-ins [edit]
Primitives (Timeline)	Functions
Scalar
		Monadic	Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
		Dyadic	Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
Non-Scalar
		Structural	Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
		Selection	First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
		Selector	Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
		Computational	Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Operators	Monadic	Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
Operators	Dyadic	Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
Quad names	Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector

[1] "Language Extensions of May 1983". SATN-45, 1983-05-02.

[1]

Stop

Documentation

References

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