add DIsplay impl for ExecutionError, CryptoError, and NetworkError

ethcore/src/types/executed.rs

@@ -21,6 +21,7 @@ use util::Bytes;
 use trace::Trace;
 use types::log_entry::LogEntry;
 use ipc::binary::BinaryConvertError;
+use std::fmt;
 use std::mem;
 use std::collections::VecDeque;
 
@@ -104,6 +105,39 @@ pub enum ExecutionError {
 	TransactionMalformed(String),
 }
 
+impl fmt::Display for ExecutionError {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		use self::ExecutionError::*;
+
+		let msg = match *self {
+			NotEnoughBaseGas { required, got } => {
+				format!("Not enough base gas. {} is required, but only {} paid",
+					required, got)
+			}
+			BlockGasLimitReached { gas_limit, gas_used, gas } => {
+				format!("Block gas limit reached. The limit is {}, {} has \
+					already been used, and {} more is required",
+					gas_limit, gas_used, gas)
+			}
+			InvalidNonce { expected, got } => {
+				format!("Invalid transaction nonce: expected {}, found {}",
+					expected, got)
+			}
+			NotEnoughCash { required, got } => {
+				format!("Cost of transaction exceeds sender balance. {} is required \
+					but the sender only has {}", required, got)
+			}
+			Internal => {
+				"Internal evm error".into()
+			}
+			TransactionMalformed(ref err) => {
+				format!("Malformed transaction: {}", err)
+			}
+		};
+
+		f.write_fmt(format_args!("Transaction execution error ({}).", msg))
+	}
+}
 
 /// Transaction execution result.
 pub type ExecutionResult = Result<Executed, ExecutionError>;