Remove variables that start with an underscore

exercises/diffie-hellman/src/lib.rs

@@ -1,11 +1,11 @@
-pub fn private_key(_p: u64) -> u64 {
-    unimplemented!()
+pub fn private_key(p: u64) -> u64 {
+    unimplemented!("Pick a private key greater than 1 and less than {}", p)
 }
 
-pub fn public_key(_p: u64, _g: u64, _a: u64) -> u64 {
-    unimplemented!()
+pub fn public_key(p: u64, g: u64, a: u64) -> u64 {
+    unimplemented!("Calculate public key using prime numbers {} and {}, and private key {}", p, g, a)
 }
 
-pub fn secret(_p: u64, _b_pub: u64, _a: u64) -> u64 {
-    unimplemented!()
+pub fn secret(p: u64, b_pub: u64, a: u64) -> u64 {
+    unimplemented!("Calculate secret key using prime number {}, public key {}, and private key {}", p, b_pub, a)
 }

exercises/isbn-verifier/src/lib.rs

@@ -1,4 +1,4 @@
 /// Determines whether the supplied string is a valid ISBN number
-pub fn is_valid_isbn(_isbn: &str) -> bool {
-    unimplemented!();
+pub fn is_valid_isbn(isbn: &str) -> bool {
+    unimplemented!("Is {:?} a valid ISBN number?", isbn);
 }

exercises/series/src/lib.rs

@@ -1,3 +1,3 @@
-pub fn series(_digits: &str, _len: usize) -> Vec<String> {
-    unimplemented!()
+pub fn series(digits: &str, len: usize) -> Vec<String> {
+    unimplemented!("What are the series of length {} in string {:?}", len, digits)
 }