Finish implementing initial Simulation interface

eth2/simulation/Cargo.toml

@@ -5,6 +5,11 @@ authors = ["Greg Trowbridge <[email protected]>"]
 edition = "2018"
 
 [dependencies]
+ewasm = "0.2.2"
 snafu = "0.6.0"
+ssz_types = { path = "../utils/ssz_types" }
 types = { path = "../types" }
+typenum = "1.11.2"
 
+[dev-dependencies]
+hex = "0.4.0"

eth2/simulation/src/lib.rs

@@ -1,3 +1,36 @@
-mod errors;
 mod simulation;
 mod store;
+
+use snafu::Snafu;
+use std::fmt;
+
+/// Shorthand for result types returned from the Simulation simulation.
+pub type Result<V, E = Error> = std::result::Result<V, E>;
+
+#[derive(Debug)]
+pub enum WhatBound {
+    ExecutionEnvironment,
+    ExecutionEnvironmentState,
+    ShardBlock(usize),
+    Shard,
+}
+
+impl fmt::Display for WhatBound {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            WhatBound::ExecutionEnvironment => write!(f, "execution environment"),
+            WhatBound::ExecutionEnvironmentState => write!(f, "execution environment state"),
+            WhatBound::Shard => write!(f, "shard"),
+            WhatBound::ShardBlock(shard) => write!(f, "block on shard {}", shard),
+        }
+    }
+}
+
+/// Errors arising from the simulation.
+#[derive(Debug, Snafu)]
+pub enum Error {
+    #[snafu(display("{} exceeds max allowable length", what))]
+    MaxLengthExceeded { what: String },
+    #[snafu(display("no {} exists at index: {}", what, index))]
+    OutOfBounds { what: WhatBound, index: usize },
+}