Pre: add mentat_query_algebrizer::errors.

query-algebrizer/Cargo.toml

@@ -4,6 +4,8 @@ version = "0.0.1"
 workspace = ".."
 
 [dependencies]
+error-chain = "0.9.0"
+
 [dependencies.mentat_core]
 path = "../core"
 

query-algebrizer/src/cc.rs

@@ -14,8 +14,8 @@ extern crate mentat_query;
 use std::fmt::{
     Debug,
     Formatter,
-    Result,
 };
+
 use std::collections::{
     BTreeMap,
     BTreeSet,
@@ -39,6 +39,12 @@ use self::mentat_query::{
     Variable,
 };
 
+use errors::{
+    Error,
+    ErrorKind,
+    Result,
+};
+
 use types::{
     DatomsColumn,
     DatomsTable,
@@ -192,7 +198,7 @@ pub enum EmptyBecause {
 }
 
 impl Debug for EmptyBecause {
-    fn fmt(&self, f: &mut Formatter) -> Result {
+    fn fmt(&self, f: &mut Formatter) -> ::std::fmt::Result {
         use self::EmptyBecause::*;
         match self {
             &TypeMismatch(ref var, ref existing, ref desired) => {
@@ -223,7 +229,7 @@ impl Debug for EmptyBecause {
 }
 
 impl Debug for ConjoiningClauses {
-    fn fmt(&self, fmt: &mut Formatter) -> Result {
+    fn fmt(&self, fmt: &mut Formatter) -> ::std::fmt::Result {
         fmt.debug_struct("ConjoiningClauses")
             .field("is_known_empty", &self.is_known_empty)
             .field("from", &self.from)

query-algebrizer/src/errors.rs

@@ -0,0 +1,40 @@
+// Copyright 2016 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+extern crate mentat_query;
+
+use self::mentat_query::{
+    PlainSymbol,
+    Variable,
+};
+
+error_chain! {
+    types {
+        Error, ErrorKind, ResultExt, Result;
+    }
+
+    errors {
+        UnknownFunction(name: PlainSymbol) {
+            description("no such function")
+            display("no function named {}", name)
+        }
+    
+        InvalidNumberOfArguments(name: PlainSymbol, number: usize, expected: usize) {
+            description("invalid number of arguments")
+            display("invalid number of arguments to {}: expected {}, got {}.", name, expected, number)
+        }
+
+        UnboundVariable(var: Variable) {
+            description("unbound variable in function call")
+            display("unbound variable: {}", var.0)
+        }
+    }
+}
+

query-algebrizer/src/lib.rs

@@ -8,9 +8,13 @@
 // CONDITIONS OF ANY KIND, either express or implied. See the License for the
 // specific language governing permissions and limitations under the License.
 
+#[macro_use]
+extern crate error_chain;
+
 extern crate mentat_core;
 extern crate mentat_query;
 
+mod errors;
 mod types;
 mod cc;