From 9a3b5a1d5f711cf4762921be79cbf7df56d36323 Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Sun, 26 Dec 2021 22:21:27 -0500 Subject: Add Array Cast link to J hook discussion --- docs/commentary/why.html | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'docs') diff --git a/docs/commentary/why.html b/docs/commentary/why.html index 77048ae3..d559b8ef 100644 --- a/docs/commentary/why.html +++ b/docs/commentary/why.html @@ -42,7 +42,7 @@

J uses numeric codes; BQN uses mostly names. So J's 1&o. is BQN's •math.Sin, and 6!:9 corresponds to BQN's •MonoTime.

J uses bytestrings by default, making Unicode handling a significant difficulty (see u:). BQN strings are lists of codepoints, so you don't have to worry about how they're encoded or fight to avoid splitting up UTF-8 bytes that need to go together.

But J has its type advantages as well. I miss complex number support in BQN, as it's an optional extension that we haven't yet implemented. And BQN has a hard rule that only one numeric type is exposed to the programmer, which means high-precision integers and rationals aren't allowed at all for a float-based implementation. I think this rule is worth it because J's implicit type conversion is hard to predict and an unexpected numeric type can cause sporadic or subtle program errors.

-

BQN uses a modifier ⟜ for J's hook, adding ⊸ for a reversed version (which I use nearly twice as often). This frees up the 2-train, which is made equivalent to Atop (∘). It's the system Roger Hui came to advocate, since he argued in favor of a hook conjunction here and made 2-train an Atop when he brought it to Dyalog APL. As an example, the J hook (#~0&<:) to remove negative numbers becomes 0⊸≤⊸/ in BQN.

+

BQN uses a modifier ⟜ for J's hook, adding ⊸ for a reversed version (which I use nearly twice as often). This frees up the 2-train, which is made equivalent to Atop (∘). It's the system Roger Hui came to advocate, since he argued in favor of a hook conjunction here and made 2-train an Atop when he brought it to Dyalog APL. As an example, the J hook (#~0&<:) to remove negative numbers becomes 0⊸≤⊸/ in BQN. Hooks are also the topic of Array Cast episode 14, where the panel points out that in J, adding a verb at the far left of a dyadic train changes the rest of the train from dyadic to monadic or vice-versa, an effect that doesn't happen in BQN.

J locales are not first-class values, and BQN namespaces are. I think BQN's namespaces are a lot more convenient to construct, although it is lacking an inheritance mechanism (but J's path system can become confusing quickly). More importantly, BQN namespaces (and closures) are garbage collected. J locales leak unless manually freed by the programmer. More generally, J has no mutable data at all, and to simulate it properly you'd have to write your own tracing garbage collection as the J interpreter doesn't have any. I discussed this issue some in this J forum thread.

In J, each function has a built-in rank attribute: for example the ranks of + are 0 0 0. This rank is accessed by the "close" compositions @, &, and &.. Choosing the shorter form for the close compositions—for example @ rather than @:—is often considered a mistake within the J community. And function ranks are unreliable: consider that the ranks of ]@:+, a function that behaves just like +, are _ _ _. In BQN there aren't any close compositions at all, and no function ranks. J's &.> is simply ¨, and other close compositions, in my opinion, just aren't needed.

Gerunds are J's answer to BQN's first-class functions. For example J's (+&3)`(2&*)@.(2&|) would be written 2⊸|◶⟨+⟜3,2⊸×⟩ with a list of functions. I think lists of functions are a big improvement, since there's no need to convert between gerund and function, and no worries about arrays that just happen to be valid gerunds (worried about losing the ability to construct gerunds? Constructing tacit functions in BQN is much easier). The usability gap widens because passing J functions around either as values or gerunds has presents some highly idiosyncratic challenges, discussed below.

-- cgit v1.2.3