Added alias support

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 * Unified the syntax of commandline switches.
 
+* Added aliases.
+
 * Automatic selection of text encoding based on target platform.
 
 * **Potentially breaking change!** `scr` now refers to the default screencodes as defined for the platform.

docs/lang/syntax.md

@@ -60,6 +60,28 @@ For every variable `x` larger than a byte, extra subvariables are defined:
 
 TODO
 
+### Alias definitions
+
+`alias <alias> = <name>`
+
+Sets an alias for a global name.
+Unless shadowed by a local name, the alias will point to the given global object:
+
+    byte x
+    alias a = x
+    
+    void f() {
+        a = 5 // writes to the global variable x
+    }
+    
+    void f() {
+        byte a
+        a = 5 // writes to the local variable a
+    }
+
+Aliases can be used for variables, arrays, constants, functions, and types,
+but not for text encodings, array formats or keywords.
+
 ### Array declarations
 
 An array is a continuous sequence of bytes in memory.

src/main/scala/millfork/env/Environment.scala

@@ -228,7 +228,10 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
       if ((t ne null) && clazz.isInstance(t)) {
         t.asInstanceOf[T]
       } else {
-        ErrorReporting.fatal(s"`$name` is not a ${clazz.getSimpleName}", position)
+        t match {
+          case Alias(_, target) => root.get[T](target)
+          case _ => ErrorReporting.fatal(s"`$name` is not a ${clazz.getSimpleName}", position)
+        }
       }
     } else parent.fold {
       ErrorReporting.fatal(s"${clazz.getSimpleName} `$name` is not defined", position)
@@ -236,6 +239,8 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
       _.get[T](name, position)
     }
   }
+  
+  private def root: Environment = parent.fold(this)(_.root)  
 
   def maybeGet[T <: Thing : Manifest](name: String): Option[T] = {
     if (things.contains(name)) {
@@ -244,7 +249,10 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
       if ((t ne null) && clazz.isInstance(t)) {
         Some(t.asInstanceOf[T])
       } else {
-        None
+        t match {
+          case Alias(_, target) => root.maybeGet[T](target)
+          case _ => None
+        }
       }
     } else parent.flatMap {
       _.maybeGet[T](name)
@@ -568,6 +576,10 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
     }
   }
 
+  def registerAlias(stmt: AliasDefinitionStatement): Unit = {
+    addThing(Alias(stmt.name, stmt.target), stmt.position)
+  }
+
   def registerFunction(stmt: FunctionDeclarationStatement, options: CompilationOptions): Unit = {
     val w = get[Type]("word")
     val name = stmt.name
@@ -1062,6 +1074,7 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
       case f: FunctionDeclarationStatement => registerFunction(f, options)
       case v: VariableDeclarationStatement => registerVariable(v, options)
       case a: ArrayDeclarationStatement => registerArray(a, options)
+      case a: AliasDefinitionStatement => registerAlias(a)
       case i: ImportStatement => ()
     }
     if (options.zpRegisterSize > 0 && !things.contains("__reg")) {

src/main/scala/millfork/env/Thing.scala

@@ -9,6 +9,8 @@ sealed trait Thing {
   def name: String
 }
 
+case class Alias(name: String, target: String) extends Thing
+
 sealed trait CallableThing extends Thing
 
 sealed trait VariableLikeThing extends Thing

src/main/scala/millfork/node/Node.scala

@@ -218,6 +218,10 @@ case class ProcessedContents(processor: String, values: ArrayContents) extends A
     ProcessedContents(processor, values.replaceVariable(variableToReplace, expression))
 }
 
+case class AliasDefinitionStatement(name: String, target: String) extends DeclarationStatement {
+  override def getAllExpressions: List[Expression] = Nil
+}
+
 case class ArrayDeclarationStatement(name: String,
                                      bank: Option[String],
                                      length: Option[Expression],

src/main/scala/millfork/parser/MfParser.scala

@@ -163,6 +163,12 @@ abstract class MfParser[T](filename: String, input: String, currentDirectory: St
 
   def arrayContentsForAsm: P[RawBytesStatement] = (arrayListContents | arrayStringContents).map(RawBytesStatement)
 
+  val aliasDefinition: P[Seq[AliasDefinitionStatement]] = for {
+    p <- position()
+    name <- "alias" ~ !letterOrDigit ~/ SWS ~ identifier ~ HWS
+    target <- "=" ~/ HWS ~/ identifier ~/ HWS
+  } yield Seq(AliasDefinitionStatement(name, target).pos(p))
+
   val arrayDefinition: P[Seq[ArrayDeclarationStatement]] = for {
     p <- position()
     bank <- bankDeclaration
@@ -366,7 +372,7 @@ abstract class MfParser[T](filename: String, input: String, currentDirectory: St
 
   val program: Parser[Program] = for {
     _ <- Start ~/ AWS ~/ Pass
-    definitions <- (importStatement | arrayDefinition | functionDefinition | globalVariableDefinition).rep(sep = EOL)
+    definitions <- (importStatement | arrayDefinition | aliasDefinition | functionDefinition | globalVariableDefinition).rep(sep = EOL)
     _ <- AWS ~ End
   } yield Program(definitions.flatten.toList)
 

src/test/java/com/grapeshot/halfnes/CPURAM.java

@@ -74,7 +74,7 @@ public class CPURAM {
     public final void write(int addr, int data) {
         addr &= 0xffff;
         if (!mem.writeable()[addr]) {
-            throw new RuntimeException("Can't write to $" + Integer.toHexString(addr));
+            throw new RuntimeException("Can't write $" + Integer.toHexString(data & 0xff) + "to $" + Integer.toHexString(addr));
         }
         mem.output()[addr] = (byte) data;
     }

src/test/scala/millfork/test/BasicSymonTest.scala

@@ -149,4 +149,23 @@ class BasicSymonTest extends FunSuite with Matchers {
         | }
       """.stripMargin){ m => () }
   }
+
+  test("Alias test") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos)(
+      """
+        | alias small = byte
+        | alias big = word
+        | byte crash @$bfff
+        | void main () {
+        |   big w
+        |   small b
+        |   b = 1
+        |   w = 1
+        |   b <<= 8
+        |   w <<= 8
+        |   if b != 0 { crash = 1 }
+        |   if w == 0 { crash = 2 }
+        | }
+      """.stripMargin){ m => () }
+  }
 }