Comparison of APL dialects

All APL dialects share core features, and at least the primitives are backwards compatible with those of APL.SV. However, there are important dialectal differences, the most significant of which are described in this article.

Flat versus Nested

One of the most significant differences between APLs is the choice of array model, namely nested or flat. Originally, all APLs were entirely flat, that is, the only scalar values supported were simple and had to be either numbers and characters, and an array had to be homogeneous, that is, consisting entirely of a single type. SHARP APL introduced the box as a third type, such that a box could hold any other array (including a box array), and this allowed for arrays contain other arrays. NARS introduced the nested array model, where any arrays can be an actual element of another array. Most currently maintained dialects (Dyalog APL, NARS2000, APL2, GNU APL, and others) use the nested array model.

Disclose

Disclose is defined, on scalars, to be the inverse of Enclose, giving the sole element of that scalar. This behavior is extended to arbitrary arrays in one of two ways: Mix, which combines all elements, and First, which returns only the first (in ravel order).

In the SHARP APL family, Disclose is written >, and given a function rank of 0, which causes it to behave as Mix. First is not a primitive.

In nested APL dialects, Disclose is written ⊃, and it was extended to First by NARS and to Mix by APL2. The other possible meaning is given the glyph ↑ and named "Mix" or "First" (not "Disclose") as appropriate. Dialects might choose either assignment of glyphs, and Dyalog APL and APL*PLUS allow either to be chosen based on Migration Level.

Glyph	Meaning	Dialects
>	Mix	SHARP APL, A, A+
⊃	Mix	APL2, ISO/IEC 13751:2001, APLX, NARS2000, GNU APL, Kap
⊃	First	ngn/apl, Co-dfns, dzaima/APL, April
⊃	Configurable	Dyalog APL, APL*PLUS, APL+Win, APL64

Complex numbers

Most dialects support complex numbers, but some (dzaima/APL, APLX, APL+Win) don't. Dialects with complex numbers also extend Circular (○) to left arguments designed for complex numbers.

Conformability

All APLs implement scalar extension in scalar dyadic functions, and Each if present. However, a few dialects differ in their support for singleton extension. Most support it fully, so that a singleton of any rank is extended. APL2 supports it only for scalars and one-element vectors (and ISO/IEC_13751:2001 specifies only this behavior), and dzaima/APL and Kap support scalar extension only.

Furthermore, dialects that implement the Rank operator differ in their conformability rules for frames. Dyalog APL and SHARP APL implement scalar agreement only, NARS2000 implements singleton agreement, and A+ implements leading axis agreement (in addition to extra options allowing the programmer to specify outer-product-like treatment of some axes).

Depth

Dyalog APL defines Depth (≡) to return negative numbers when the depth is uneven. Most other dialects instead define it to return the maximum depth. The original NARS paper assigned the glyph to a function called Simple, which simply answered if the argument was simple or not, without reporting the actual depth. It was thus equivalent to today's 1=≡,Y.

Language features

The following table shows support for various APL features: nesting either with boxes or the nested array model, defined functions or similar syntax, control structures, dfn-style anonymous functions, tacit programming, particularly with trains, complex numbers, arbitrary-precision integers, Unicode support, and namespaces or a similar encapsulation feature. The precise syntax and capabilities of these features might differ between dialects that support them.

Dialects included in the first row include APL\360, APL\1130, APL*PLUS before II, APL/700, APL.SV, APL 5100, MCM/70, VS APL, APL\3000, and Aplette. Extended Dyalog APL and Dyalog APL Vision have the same feature-set as Dyalog APL.

Dialect	Nesting	Tradfns	Control	Dfns	Tacit	Complex	Big int	Unicode	Namespace
APL\360, APL.SV, …	No	Yes	No	No	No	No	No	No	No
SHARP APL	Boxes	Yes	No	No	No	Yes	No	No	No
NARS	Nested	Yes	No	direct def	No	No	No	No	No
Dyalog APL	Nested	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes
APL2	Nested	Yes	No	No	No	Yes	No	No	Yes
A+	Boxes	Yes	Yes	No	Some	No	No	No	No
APL*PLUS II	Nested	Yes	No	No	No	No	No	No	No
SAX	Boxes	Yes	Yes	No	Some	No	No	No	No
APL*PLUS III	Nested	Yes	Yes	No	No	No	No	No	No
APL+Win	Nested	Yes	Yes	No	No	No	No	No	Yes
APLX	Nested	Yes	Yes	No	No	No	No	No	No
NARS2000	Nested	Yes	Yes	Yes	Yes	Yes	Yes	UCS-2	No
VisualAPL	Nested	Yes	Yes	No	No	No	No	Yes	Yes
APL#	Nested	No	Yes	Yes	Yes	No	No	Yes	Yes
ngn/apl	Nested	No	No	Yes	Yes	Yes	No	Yes	No
GNU APL	Nested	Yes	If-else	Limited	No	Yes	Yes	Yes	Yes
Co-dfns	Nested	No	No	Yes	Yes	Yes	No	Yes	Partial
April	Nested	No	No	Yes	Yes	Yes	Yes	Yes	Yes
dzaima/APL	Nested	No	No	Yes	Yes	No	Yes	Yes	No
APL\iv	Lists	No	No	Yes	Yes	Yes	No	Yes	No
Kap	Nested	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
APL64	Nested	Yes	Yes	No	No	No	No	Yes	Yes

External links

• Omnibar lists all glyphs with their meanings and allows custom comparisons between dialects:
  File:Omnibar