Add import statement (#57)

README.md

@@ -174,7 +174,9 @@ assertEquals(onePlusOne, anotherOnePlusOne)
 // Top level
 type_universe ::= <stmt>...
 definition ::= '(' 'define' symbol <domain_definition> ')'
-stmt ::=  <definition> | <transform>
+stmt ::=  <definition> | <transform> | <include>
+
+import ::= `(import <path-to-include)`
 
 // Domain
 domain_definition ::= <domain> | <permute_domain>
@@ -400,6 +402,20 @@ Unlike record elements, product element defintions must include identifiers.
 (product int_pair first::int second::int)
 ```
 
+#### Imports
+
+It is possible to split type universe definitions among multiple files:
+
+```
+// root.ion:
+(import "a.ion")
+(import "b.ion")
+```
+
+The resulting type universe will contain all type domains from both `a.ion` and `b.ion`, `root.ion` may also 
+define additional type domains.  The primary purpose of this is to be able to permute domains defined in another 
+file.
+
 
 #### Using PIG In Your Project
 

pig/src/org/partiql/pig/cmdline/Command.kt

@@ -20,5 +20,5 @@ import java.io.File
 sealed class Command {
     object ShowHelp : Command()
     data class InvalidCommandLineArguments(val message: String) : Command()
-    data class Generate(val typeUniverseFile: File, val outputFile: File, val target: TargetLanguage) : Command()
+    data class Generate(val typeUniverseFile: String, val outputFile: String, val target: TargetLanguage) : Command()
 }

pig/src/org/partiql/pig/cmdline/CommandLineParser.kt

@@ -145,7 +145,7 @@ class CommandLineParser {
                         LanguageTargetType.CUSTOM -> TargetLanguage.Custom(optSet.valueOf(templateOpt))
                     }
 
-                    Command.Generate(typeUniverseFile, outputFile, target)
+                    Command.Generate(typeUniverseFile.toString(), outputFile.toString(), target)
                 }
             }
         } catch(ex: OptionException) {

pig/src/org/partiql/pig/domain/model/SemanticErrorContext.kt

@@ -18,6 +18,8 @@ package org.partiql.pig.domain.model
 import com.amazon.ionelement.api.IonLocation
 import com.amazon.ionelement.api.MetaContainer
 import com.amazon.ionelement.api.location
+import org.partiql.pig.domain.parser.SourceLocation
+import org.partiql.pig.domain.parser.sourceLocation
 import org.partiql.pig.errors.PigException
 import org.partiql.pig.errors.ErrorContext
 import org.partiql.pig.errors.PigError
@@ -109,9 +111,9 @@ sealed class SemanticErrorContext(val msgFormatter: () -> String): ErrorContext
  * Shortcut for throwing [PigException] with the specified metas and [PigError].
  */
 fun semanticError(blame: MetaContainer, context: ErrorContext): Nothing =
-    semanticError(blame.location, context)
+    semanticError(blame.sourceLocation, context)
 /**
  * Shortcut for throwing [PigException] with the specified metas and [PigError].
  */
-fun semanticError(blame: IonLocation?, context: ErrorContext): Nothing =
+fun semanticError(blame: SourceLocation?, context: ErrorContext): Nothing =
     throw PigException(PigError(blame, context))

pig/src/org/partiql/pig/domain/parser/ImportSourceOpener.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * or in the "license" file accompanying this file. This file 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.
+ */
+
+package org.partiql.pig.domain.parser
+
+import com.amazon.ion.IonReader
+import com.amazon.ion.system.IonReaderBuilder
+import java.io.Closeable
+import java.io.File
+import java.io.FileInputStream
+import java.nio.file.Path
+
+//class ImportSource(
+//    val fullyQualifiedName: String,
+//    val reader: IonReader
+//) : Closeable {
+//    override fun close() {
+//        reader.close()
+//    }
+//}
+
+// TODO: names

pig/src/org/partiql/pig/domain/parser/InputSource.kt

@@ -0,0 +1,45 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * or in the "license" file accompanying this file. This file 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.
+ */
+
+package org.partiql.pig.domain.parser
+
+import java.io.File
+import java.io.FileInputStream
+import java.io.InputStream
+
+/**
+ * Provides an abstraction for file-system related functions used when importing files.
+ */
+internal interface InputSource {
+    /**
+     * Opens an input stream for the given source name.
+     *
+     * The [sourceName] is implementation-defined.  In the case of a file system implementaiton it is the path to a
+     * file, either relative to the working directory or absolute.
+     */
+    fun openStream(sourceName: String): InputStream
+
+    /**
+     * Returns the "canonical name" of the given source.  In the case of a file system, this converts the relative
+     * path to an absolute path.
+     */
+    fun getCanonicalName(sourceName: String): String
+}
+
+internal val FILE_SYSTEM_SOURCE = object : InputSource {
+    override fun openStream(qualifiedSource: String) = FileInputStream(qualifiedSource)
+
+    override fun getCanonicalName(sourceName: String): String = File(sourceName).canonicalFile.toString()
+}

pig/src/org/partiql/pig/domain/parser/ParserErrorContext.kt

@@ -42,6 +42,9 @@ sealed class ParserErrorContext(val msgFormatter: () -> String): ErrorContext {
         override fun hashCode(): Int = 0
     }
 
+    data class CouldNotFindImportedTypeUniverse(val tag: String)
+        : ParserErrorContext({ "Could not find imported type universe: $tag" })
+
     data class UnknownConstructor(val tag: String)
         : ParserErrorContext({ "Unknown constructor: '$tag' (expected constructors are 'domain' or 'permute_domain')" })
 
@@ -79,8 +82,7 @@ sealed class ParserErrorContext(val msgFormatter: () -> String): ErrorContext {
         : ParserErrorContext({ "Element has multiple name annotations"})
 }
 
-
-fun parseError(blame: IonLocation?, context: ErrorContext): Nothing =
+fun parseError(blame: SourceLocation?, context: ErrorContext): Nothing =
     PigError(blame, context).let {
         throw when (context) {
             is ParserErrorContext.IonElementError -> {
@@ -91,8 +93,3 @@ fun parseError(blame: IonLocation?, context: ErrorContext): Nothing =
         }
     }
 
-fun parseError(blame: IonElement, context: ErrorContext): Nothing {
-    val loc = blame.metas.location
-    parseError(loc, context)
-}
-

pig/src/org/partiql/pig/domain/parser/SourceLocation.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * or in the "license" file accompanying this file. This file 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.
+ */
+
+package org.partiql.pig.domain.parser
+
+import com.amazon.ionelement.api.IonLocation
+import com.amazon.ionelement.api.MetaContainer
+
+/**
+ * Includes path to a source file and a position within it.
+ *
+ * Used to construct helpful error messages for the end-user, who will be able to know the file, line & column of
+ * a given error.
+ */
+data class SourceLocation(val path: String, val location: IonLocation) {
+    override fun toString(): String {
+        return "$path:$location"
+    }
+}
+
+internal const val SOURCE_LOCATION_META_TAG = "\$pig_source_location"
+
+internal val MetaContainer.sourceLocation
+    get() = this[SOURCE_LOCATION_META_TAG] as? SourceLocation