From 55c40e75dde0ddad39a305f29e036ec88c85babe Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Wed, 2 Dec 2020 14:45:59 -0500 Subject: Move problems.md to commentary folder --- docs/doc/context.html | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'docs/doc/context.html') diff --git a/docs/doc/context.html b/docs/doc/context.html index 1b5e949c..8c0ea92e 100644 --- a/docs/doc/context.html +++ b/docs/doc/context.html @@ -17,7 +17,7 @@

Here, the lowercase spelling indicates that a and e are to be treated as subjects ("arrays" in APL) while the uppercase spelling of variables B and C are used as functions and _d is a 1-modifier ("monadic operator"). Like parentheses for function application, the spelling is not inherent to the variable values used, but instead indicates their grammatical role in this particular expression. A variable has no inherent spelling and can be used in any role, so the names a, A, _a, and _a_ all refer to exact same variable, but in different roles; typically we use the lowercase name to refer to the variable in isolation—all values are nouns when speaking about them in English. While we still don't know anything about what values a, b, c, and so on have, we know how they interact in the line of code above.

Is grammatical context really a problem?

-

Yes, in the sense of problems with BQN. A grammar that uses context is harder for humans to read and machines to execute. A particular difficulty is that parts of an expression you don't yet understand can interfere with parts you do, making it difficult to work through an unknown codebase.

+

Yes, in the sense of problems with BQN. A grammar that uses context is harder for humans to read and machines to execute. A particular difficulty is that parts of an expression you don't yet understand can interfere with parts you do, making it difficult to work through an unknown codebase.

One difficulty beginners to APL will encounter is that code in APL at first appears like a string of undifferentiated symbols. For example, a tacit Unique Mask implementation ⍳⍨=⍳∘≢ consists of six largely unfamiliar characters with little to distinguish them (in fact, the one obvious bit of structure, the repeated ⍳, is misleading as it means different things in each case!). Simply placing parentheses into the expression, like (⍳⍨)=(⍳∘≢), can be a great help to a beginner, and part of learning APL is to naturally see where the parentheses should go. The equivalent BQN expression, ⊐˜=↕∘≠, will likely appear equally intimidating at first, but the path to learning which things apply to which is much shorter: rather than learning the entire list of APL primitives, a beginner just needs to know that superscript characters like ˜ are 1-modifiers and characters like ∘ with unbroken circles are 2-modifiers before beginning to learn the BQN grammar that will explain how to tie the various parts together.

This sounds like a distant concern to a master of APL or a computer that has no difficulty memorizing a few dozen glyphs. Quite the opposite: the same concern applies to variables whenever you begin work with an unfamiliar codebase! Many APL programmers even enforce variable name conventions to ensure they know the class of a variable. By having such a system built in, BQN keeps you from having to rely on programmers following a style guide, and also allows greater flexibility, including functional programming, as we'll see later.

Shouldn't a codebase define all the variables it uses, so we can see their class from the definition? Not always: consider that in a language with libraries, code might be imported from dependencies. Many APLs also have some dynamic features that can allow a variable to have more than one class, such as the ⍺←⊢ pattern in a dfn that makes ⍺ an array in the dyadic case but a function in the monadic case. Regardless, searching for a definition somewhere in the code is certainly a lot more work than knowing the class just from looking! One final difficulty is that even one unknown can delay understanding of an entire expression. Suppose in A B c, B is a function and c is an array, and both values are known to be constant. If A is known to be a function (even if its value is not yet known), its right argument B c can be evaluated ahead of time. But if A's type isn't known, it's impossible to know if this optimization is worth it, because if it is an array, B will instead be called dyadically.

-- cgit v1.2.3