Allow omitting length in file array initalizers (fixes #35)

docs/lang/literals.md

@@ -175,6 +175,7 @@ An array is initialized with either:
         array b = "----" scr
         array c = ["hello world!" ascii, 13]
         array d = file("d.bin")
+        array d1 = file("d.bin", 128)
         array e = file("d.bin", 128, 256)
         array f = for x,0,until,8 [x * 3 + 5]  // equivalent to [5, 8, 11, 14, 17, 20, 23, 26]
         array(point) g = [point(2,3), point(5,6)]
@@ -183,7 +184,10 @@ An array is initialized with either:
 Trailing commas (`[1, 2,]`) are not allowed.
 
 The parameters for `file` are: file path, optional start offset, optional length
-(start offset and length have to be either both present or both absent).
+(if only two parameters are present, then the second one is assumed to be the start offset).
+The `file` expression is expanded at the compile time to an array of bytes equal to the bytes contained in the file.
+If the start offset is present, then that many bytes at the start of the file are skipped.
+If the length is present, then only that many bytes are taken, otherwise, all bytes until the end of the file are taken. 
 
 The `for`-style expression has a variable, a starting index, a direction, a final index, 
 and a parameterizable array initializer.

examples/nes/pong.mfk

@@ -627,4 +627,4 @@ const array attribute = [
 
 
 //  *CHARACTER ROM (GRAPHICS)*
-segment(chrrom) const array graphics @ $0000 = file("tiles.chr")
+segment(chrrom) const array graphics @ $0000 = file("tiles.chr", 0)

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

@@ -229,12 +229,31 @@ abstract class MfParser[T](fileId: String, input: String, currentDirectory: Stri
   val arrayFileContents: P[ArrayContents] = for {
     p <- "file" ~ HWS ~/ "(" ~/ HWS ~/ position("file name")
     filePath <- doubleQuotedString ~/ HWS
-    optSlice <- ("," ~/ HWS ~/ literalAtom ~/ HWS ~/ "," ~/ HWS ~/ literalAtom ~/ HWS ~/ Pass).?
+    optStart <- ("," ~/ HWS ~/ literalAtom ~/ HWS ~/ Pass).?
+    optLength <- ("," ~/ HWS ~/ literalAtom ~/ HWS ~/ Pass).?
     _ <- ")" ~/ Pass
   } yield {
     val data = Files.readAllBytes(Paths.get(currentDirectory, filePath))
-    val slice = optSlice.fold(data) {
-      case (start, length) => data.slice(start.value.toInt, start.value.toInt + length.value.toInt)
+    val slice: Array[Byte] = (optStart.map(_.value.toInt), optLength.map(_.value.toInt)) match {
+      case (Some(start), Some(length)) =>
+        if (data.length < start) {
+          log.error(s"File $filePath is shorter (${data.length} B) that the start offset $start", Some(p))
+          Array.fill(length)(0.toByte)
+        } else if (data.length < start + length) {
+          log.error(s"File $filePath is shorter (${data.length} B) that the start offset plus length ${start + length}", Some(p))
+          Array.fill(length)(0.toByte)
+        } else {
+          data.slice(start, start + length)
+        }
+      case (Some(start), None) =>
+        if (data.length < start) {
+          log.error(s"File $filePath is shorter (${data.length} B) that the start offset $start", Some(p))
+          Array[Byte](0)
+        } else {
+          data.drop(start)
+        }
+      case (None, None) => data
+      case _ => throw new IllegalStateException("error parsing file()")
     }
     LiteralContents(slice.map(c => LiteralExpression(c & 0xff, 1)).toList)
   }