quote - bad

8.12

quote - bad🔗ℹ

source code: https://github.com/AlexKnauth/quote-bad

1 Replacing bad uses of quote in programs

2 Changing the printing style to avoid printing bad uses of quote

1 Replacing bad uses of quote in programs🔗ℹ

The quote form can seem convenient as a shorthand, but it can lead to many common mistakes. Most of these mistakes come from people not understanding that a quoted form also quotes its sub-expressions.

In a file that requires this library, using quote for compound data will cause an error with a message telling you how to write it without quote, and "self-quoting" compound data literals such as vector literals will display a similar error explaining how to write the same thing without them.

Examples:

> (require quote-bad/quote-bad)
> 'hello
'hello
> '"this is fine"
"this is fine"
> '#:of-course
'#:of-course
> '(1 2 (+ 1 2))
eval:7:0: quote: Don't use quote for this. Instead you can
use
(list 1 2 (list '+ 1 2))
in: (quote (1 2 (+ 1 2)))
> (list 1 2 (list '+ 1 2))
(list 1 2 (list '+ 1 2))
> (list 1 2 (+ 1 2))
(list 1 2 3)
> #(1 2 (+ 1 2))
eval:10:0: #%datum: Don't use self-quoting compound literals
that implicitly quote sub-expressions.
Instead you can use
(vector-immutable 1 2 (list '+ 1 2))
in: (#%datum . #(1 2 (+ 1 2)))
> (vector-immutable 1 2 (list '+ 1 2))
(vector-immutable 1 2 (list '+ 1 2))
> (vector-immutable 1 2 (+ 1 2))
(vector-immutable 1 2 3)

Unfortunately, this doesn’t do anything about printing (yet), so depending on your settings, values like lists, vectors, etc. could still print with quote.

Note that this does not do anything to quasiquote, so if there any expressions that really do make sense as quoted, you can quasiquote them instead.

syntax
(quote datum)

Like racket’s quote form, except that for compound literal data it displays an error message explaining how to write the expression without quote.

syntax
(#%datum . datum)

A form implicitly inserted for literals. This version expands to quote for simple atomic data such as numbers, strings, and booleans, but for self-quoting compound data such as vector literals, it displays an error message explaining how to write the expression without using self-quoting literals.

2 Changing the printing style to avoid printing bad uses of quote🔗ℹ

#lang constructor-style-print

package: quote-bad

A lang-extension like at-exp that changes the printing style for programs that use it in the main file. The lang line #lang constructor-style-print racket declares a language like racket, except that values are printed using constructor-style printing instead of with quote.

Instead of '(1 2 3), a list would print as (list 1 2 3). Instead of '#(1 2 3), a mutable vector would print as (vector 1 2 3), and an immutable vector would print as (vector-immutable 1 2 3).

But most importantly, a nested structure like '(1 2 (+ 1 2)) would print as (list 1 2 (list '+ 1 2)), showing the nested uses of the constructors.

Examples:

> (require racket/vector)
> 'hello
'hello
> (list 1 2 (+ 1 2))
(list 1 2 3)
> '(1 2 (+ 1 2))
(list 1 2 (list '+ 1 2))
> (vector-immutable 1 2 (+ 1 2))
(vector-immutable 1 2 3)
> #(1 2 (+ 1 2))
(vector-immutable 1 2 (list '+ 1 2))
> (vector 1 2 (+ 1 2))
(vector 1 2 3)
> (vector-copy #(1 2 (+ 1 2)))
(vector 1 2 (list '+ 1 2))

1	Replacing bad uses of quote in programs
2	Changing the printing style to avoid printing bad uses of quote