Function set_preference

src/interface.rs:188–239

Set a MathCAT preference. The preference name should be a known preference name. The value should either be a string or a number (depending upon the preference being set) The list of known user preferences is in the MathCAT user documentation. Here are common preferences set by programs (not settable by the user): TTS -- SSML, SAPI5, None Pitch -- normalized at '1.0' Rate -- words per minute (shou

(name: String, value: String)

/// 
/// Be careful setting preferences -- these potentially override user settings, so only preferences that really need setting should be set.
pub fn set_preference(name: String, value: String) -> Result<()> {
    let old_value = get_preference(name.clone())?;      // make sure it is a valid preference
    
    if name == "Language" {
        // check the format
        if !( value == "Auto" ||
                value.len() == 2 ||
                (value.len() == 5 && value.as_bytes()[2] == b'-') ) {
            bail!("Improper format for 'Language' preference '{}'. Should be of form 'en' or 'en-gb'", value);
        }
    }
    
    crate::speech::SPEECH_RULES.with(|rules| {
        let rules = rules.borrow_mut();
        if let Some(error_string) = rules.get_error() {
            bail!("{}", error_string);
        }

        // we set the value even if it was the same as the old value because this might override a potentially changed future user value
        let mut pref_manager = rules.pref_manager.borrow_mut();
        let lower_case_value = value.to_lowercase();
        if lower_case_value == "true" || lower_case_value == "false" {
            pref_manager.set_api_boolean_pref(&name, value.to_lowercase()=="true"); 
        } else { 
            match name.as_str() {
                "Pitch" | "Rate" | "Volume" | "CapitalLetters_Pitch"=> {
                    pref_manager.set_api_float_pref(&name, to_float(&name, &value)?);    
                },
                _ => {
                    pref_manager.set_api_string_pref(&name, &value);
                },
            }
        };
        return Ok::<(), Error>( () );
    })?;

    if old_value == value {
        return Ok( () );            // nothing changed
    }

    if let Some(changed) = FilesChanged::new(&name) {
        crate::speech::SpeechRules::invalidate(changed);
    }
    return Ok( () );

    fn to_float(name: &str, value: &str) -> Result<f64> {
        return match value.parse::<f64>() {
            Ok(val) => Ok(val),
            Err(_) => bail!("SetPreference: preference'{}'s value '{}' must be a float", name, value),
        };
    }
}

/// Get the braille associated with the MathML that was set by [`set_mathml`].
/// The braille returned depends upon the preference for the `code` preference (default `Nemeth`).