Function core_char 

pub fn core_char(c: &char) -> Option<char>

The function helps giving the core text of a greek new testament critical edition.
This might be useful for comparing greek new testament critical editions by gettig their “core” differences/concordances.

In concrete terms, core_char remove any character that is not in the greek alphabet, puts all greek letters in lowercase, and change all sigmas to lunar sigma.

So this function :

• does not replace nomina sacras (e.g., κϲ) by their non-abreviated form (resp. κυριοϲ), nor words (e.g., κύριος) by their nomina sacras form (when a nomina sacra form exists) (resp. κϲ).
• is made to delete any character used to encode nomina sacras (e.g., ‘|’, or ‘(’ and ‘)’), hence |κς| will give κϲ.
• does delete all ‘ˉ’ characters (so παραβολὴˉ becomes παραβολη, not παραβολην) TODO : expliquer pourquoi on ne garde pas le point median.

Example :

use gnt_tools::core_char;

let s = "16 Εἶπεν δὲ παραβολὴν πρὸς αὐτοὺς λέγων·
         ἀνθρώπου τινὸς πλουσίου εὐφόρησεν ἡ χώρα. 17
         καὶ διελογίζετο ἐν ἑαυτῷ λέγων· τί ποιήσω, ὅτι
         οὐκ ἔχω ποῦ συνάξω τοὺς καρπούς μου; ";

let s2 = "ειπενδεπαραβοληνπροϲαυτουϲλεγωνανθρωπουτ\
          ινοϲπλουϲιουευφορηϲενηχωρακαιδιελογιζετοενεαυτω\
          λεγωντιποιηϲωοτιουκεχωπουϲυναξωτουϲκαρπουϲμου";

let core_text : String = s.chars()
                          .filter_map(|c| core_char(&c))
                          .collect();

assert_eq!(core_text.as_str(), s2);