From 7273e5bec783772f6d61e056b5c138c70fd58663 Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Wed, 13 Apr 2022 22:28:55 -0400 Subject: Documentation for Constant --- docs/doc/constant.html | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 docs/doc/constant.html (limited to 'docs/doc/constant.html') diff --git a/docs/doc/constant.html b/docs/doc/constant.html new file mode 100644 index 00000000..524a13f5 --- /dev/null +++ b/docs/doc/constant.html @@ -0,0 +1,55 @@ + + + + BQN: Constant + +
(github) / BQN / doc
+

Constant

+ + + + Constant + + ๐•—ห™ ๐•ฉ + + + + ๐•— + ๐•ฉ + + + ๐•จ ๐•—ห™ ๐•ฉ + + + + + ๐•— + ๐•จ + ๐•ฉ + + + + +

It's one of the simple ones: fห™๐•ฉ is f. And ๐•จfห™๐•ฉ? It's f. Like the identity functions, Constant doesn't compute anything but just returns one of its inputs. It's somewhat different in that it's a deferred modifier, so you have to first apply Constant to its operand and then to some arguments for that non-event to happen.

+

The design of BQN makes Constant unnecessary in most cases, because when a non-operation (number, character, array, namespace) is applied it already returns itself: ฯ€ห™ is the same function as ฯ€. If you've used much tacit programming, you've probably written a few trains like 2ร—+ (twice the sum), which is nicer than the equivalent 2ห™ร—+. However, a train has to end with a function, so you can't just put a number at the end. Applying ห™ is a convenient way to change the number from a subject to a function role.

+โ†—๏ธ
    +รท2   # A number
+0.5
+
+    +รท2ห™  # A function
++รท2ห™
+
+    3 (+รท2ห™) 7
+5
+
+

When programming with first-class functions, the constant application shortcut becomes a hazard! Consider the program {๐•จโŒพ(2โŠธโŠ‘) ๐•ฉ} to insert ๐•จ into an array ๐•ฉ as an element. It works fine with a number, but with a function it's broken:

+โ†—๏ธ
    โˆž {๐•จโŒพ(2โŠธโŠ‘) ๐•ฉ} 1โ€ฟ2โ€ฟ3โ€ฟ4
+โŸจ 1 2 โˆž 4 โŸฉ
+
+    M โ† -
+    m {๐•จโŒพ(2โŠธโŠ‘) ๐•ฉ} 1โ€ฟ2โ€ฟ3โ€ฟ4
+โŸจ 1 2 ยฏ3 4 โŸฉ
+
+

Here m is applied to 2โŠ‘๐•ฉ even though we want to discard that value. Spelled as m, our context-free grammar knows it's a function argument, but this doesn't affect later usage. Under always applies ๐”ฝ as a function. The proper definition of the insertion function should use a ห™, like this:

+โ†—๏ธ
    m {๐•จห™โŒพ(2โŠธโŠ‘) ๐•ฉ} 1โ€ฟ2โ€ฟ3โ€ฟ4
+โŸจ 1 2 - 4 โŸฉ
+
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