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.

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.

First/Mix

In dialects implementing nested array theory, the two glyphs commonly used for Disclose are Right Shoe (⊃) and Up Arrow (↑). The original NARS paper specified monadic ↑ as Mix and ⊃ as First, so Dyalog and STSC implemented Dyalog APL and APL*PLUS accordingly. IBM decided to swap them in APL2, causing the others to implement Migration Level, as APL2 was seen as the authoritative implementation. When the ISO standard was written, it closely followed APL2, causing APLX, NARS2000, GNU APL, and ngn/apl to adopt these notations. However, ngn/apl later switched to follow Dyalog.

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.

External links

• Omnibar is a site that lists all available glyphs in a variety of dialects together with their meanings. It supports filtering using set operations (union, intersection, difference) between feature sets of the supported dialects.