1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89

//! Provides the alphabet!() macro. It can be used to create const alphabets easily.
//!
//! Usually you would have to write alphabets in a cumbersome way:
//! ```
//! const HEX: [char; 16] = ['0', '1', '2', '3',
//!     '4', '5', '6', '7',
//!     '8', '9', 'a', 'b',
//!     'c', 'd', 'e', 'f'];
//!
//! assert_eq!(HEX.len(), 16);
//! assert_eq!(HEX[5], '5');
//! assert_eq!(HEX[10], 'a');
//! ```
//!
//! But with the alphabet!() macro this can be done way easier.
//! ```
//! use alphabet_macro::alphabet;
//!
//! alphabet!(HEX = "0123456789abcdef");
//!
//! assert_eq!(HEX.len(), 16);
//! assert_eq!(HEX[5], '5');
//! assert_eq!(HEX[10], 'a');
//! ```
//!
//! The alphabet!() macro expands to the snippet above, while being easier to read, write and understand.

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse, self};

struct Alphabet {
    ident: syn::Ident,
    contents: String
}

/// Declares a constant alphabet. You can choose any valid identifier as the name for the alphabet.
///
/// The general syntax looks like alphabet!(_<name>_ = "_<contents>_").
///
/// # Examples
/// ```
/// use alphabet_macro::alphabet;
///
/// alphabet!(BINARY  = "01");
/// alphabet!(ENGLISH = "abcdefghijklmnopqrstuvwxyz");
/// alphabet!(GERMAN  = "aäbcdefghijklmnoöpqrstuüvwxyzß");
/// alphabet!(HEBREW  = "אבגדהוזחטיכלמנסעפצקרשת");
///
/// assert_eq!(BINARY.len(), 2);
/// assert_eq!(ENGLISH.len(), 26);
/// assert_eq!(GERMAN.len(), 30);
/// assert_eq!(HEBREW.len(), 22);
/// ```
#[proc_macro]
pub fn alphabet(input: TokenStream) -> TokenStream {
    let Alphabet {
        ident,
        contents
    } = syn::parse_macro_input!(input as Alphabet);

    let chars: Vec<char> = contents.chars().collect();
    let alphabet_len = chars.len();
    TokenStream::from(quote! {
        const #ident: [char; #alphabet_len] = [#(#chars),*];
    })
}

impl syn::parse::Parse for Alphabet {
    fn parse(buf: parse::ParseStream) -> syn::Result<Self> {
        // alphabet!(FOO = "abcdef0123456789");
        //           ^^^
        let ident: syn::Ident = buf.parse()?;

        // alphabet!(FOO = "abcdef0123456789");
        //               ^
        buf.parse::<syn::Token![=]>()?;

        // alphabet!(FOO = "abcdef0123456789");
        //                 ^^^^^^^^^^^^^^^^^^
        let contents: syn::LitStr = buf.parse()?;
        let contents = contents.value();

        Ok(Alphabet {
            ident,
            contents
        })
    }
}