Change object model and add crate Error type

src/transaction.rs

@@ -1,20 +1,18 @@
+use crate::Error;
+
 pub struct Transaction {
     pub date: String,
     pub payee: String,
     pub amount: i64,
 }
 
-fn parse_amount_str(amount: &str) -> Result<i64, String> {
+fn parse_amount_str(amount: &str) -> Result<i64, Error> {
     if amount.is_empty() {
-        return Err("empty amount".to_string());
+        return Err(Error::AmountEmpty);
     }
     let (whole, frac) = amount.split_once('.').unwrap_or((amount, "00"));
-    let whole = whole
-        .parse::<i64>()
-        .map_err(|e| format!("parse error on whole {}: {}", whole, e))?;
-    let frac = frac
-        .parse::<i64>()
-        .map_err(|e| format!("parse error on fraction {}: {}", frac, e))?;
+    let whole = whole.parse::<i64>()?;
+    let frac = frac.parse::<i64>()?;
 
     let mut amount: i64 = 0;
     amount += whole * 100 * 10;
@@ -24,7 +22,7 @@ fn parse_amount_str(amount: &str) -> Result<i64, String> {
 
 impl Transaction {
     /// Construct a Transaction from [date, payee, amount] strings
-    pub fn from_fields(date: &str, payee: &str, amount: &str) -> Result<Transaction, String> {
+    pub fn from_fields(date: &str, payee: &str, amount: &str) -> Result<Transaction, Error> {
         Ok(Transaction {
             date: date.to_owned(),
             payee: payee.to_owned(),