From 2afb23928e1984d475cc460e1672e8f6fa0e4dbe Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Wed, 11 Aug 2021 17:21:31 -0400 Subject: Allow clicking on header to get fragment link --- docs/doc/undo.html | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'docs/doc/undo.html') diff --git a/docs/doc/undo.html b/docs/doc/undo.html index dc3f9d37..5e7d6276 100644 --- a/docs/doc/undo.html +++ b/docs/doc/undo.html @@ -4,7 +4,7 @@ BQN: Undo
(github) / BQN / doc
-

Undo

+

Undo

Oh no, you've deleted a function after spending half an hour writing it! Well… hopefully your editor can help with that. But maybe you'll be interested to hear that BQN can reverse the action of some functions—ones that don't lose information. This capability is also used by Repeat (⍟) to repeat a negative number of times.

↗️
    2 ⌽ "abcde"
 "cdeab"
@@ -20,7 +20,7 @@
 "BQN"

Here it undoes a function to decrement the last character by incrementing that character. In part this is enabled by the clean design of BQN primitives, because better-behaved functions like those using structural Under are easier to invert.

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The rules

+

The rules

If 𝔽 can be inverted exactly, then Undo just does that. However, there are also some other functions that BQN inverts. For example, the squaring function ט has both a positive and a negative inverse, and yet:

↗️
    ט ¯3
 9
@@ -32,7 +32,7 @@
 ↗️
    6 - √⁼√6
 8.881784197001252e¯16
 

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What's supported?

+
What's supported?

 
For the full list, see the specification. An individual implementation might support a lot more functionality than is required, so if you're not concerned about portability just try out whatever function you're interested in.

 
Arithmetic and simple combinators are usually invertible. A compound function that refers to its argument just once, like 6+⌽∘⍉, can typically be undone, but one that uses the argument in two different ways, such as ⊢+⋆, probably can't.

 
A few notable inverses are the logarithm ⋆⁼, un-Transpose ⍉⁼, and Indices inverse /⁼. Enclose inverse, <⁼, is an alternative to First that requires its argument to be a unit.

@@ -42,7 +42,7 @@ ERROR
     3 ⊣⁼ 3
 3
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Undo headers

+

Undo headers

Undo headers are currently supported only by dzaima/BQN.

Of course BQN will never be able to invert all the functions you could write (if it could you could earn a lot of bitcoins, among other feats). But it does recognize some header forms that you can use to specify the inverse of a block function. BQN will trust you and won't verify the results your specified inverse gives.

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