Added #define directive

CHANGELOG.md

@@ -60,6 +60,8 @@
 
 * Preprocessor: Added `if` function
 
+* Preprocessor: Added `#define` directive.
+
 * Fixed volatile-related bugs.
 
 * Fixed optimizations removing jumps to jumps.

docs/lang/preprocessor.md

@@ -148,6 +148,15 @@ Emits a diagnostic message.
     
 Evaluates an expression and emits the result as a diagnostic message.
 
+### `#define`
+
+    #define <ident> = <expr>
+
+Defines a new feature value or redefines a previous feature value.
+
+The feature value is visible only to the preprocessor, only when processing the current file,
+and only in lines preprocessed after this one. 
+
 ### `#use`
 
     #use <ident> = <expr>

examples/crossplatform/guess.mfk

@@ -10,6 +10,8 @@ import c64_basic
 import c264_basic
 #endif
 
+#define READKEY = CBM_64 | CBM_VIC | CBM_264 | CBM_128 | ZX_SPECTRUM | NEC_PC_88 | ATARI_8
+
 void main () {
     init_rand_seed()
     ensure_mixedcase()
@@ -60,5 +62,10 @@ void play_round() {
     putword(guess_count)
     putstrz(" attempts!"z)
     new_line()
+    #if READKEY
+    putstrz("Press any key to play again."z)
+    readkey()
+    new_line()
+    #endif
     new_line()
 }

src/main/scala/millfork/parser/Preprocessor.scala

@@ -37,11 +37,12 @@ object Preprocessor {
     var enabled = true
     val ifStack = mutable.Stack[IfContext]()
     var lineNo = 0
+    var currentFeatures = options.features
 
     def evalParam(param: String, pos: Some[Position]): Long = {
       new PreprocessorParser(options).expression.parse(param) match {
         case Success(q, _) =>
-          val value = q.apply(options.features).getOrElse(0L)
+          val value = q.apply(currentFeatures).getOrElse(0L)
 //          log.trace(param + " ===> " + value)
           value
         case Failure(_, _, _) =>
@@ -50,6 +51,17 @@ object Preprocessor {
       }
     }
 
+    def assertIdentifier(ident: String, pos: Option[Position]) : String = {
+      ident.foreach{
+        case ' ' => log.error("Unexpected space in a preprocessor identifier", pos)
+        case '_' => // ok
+        case c if c < 128 && Character.isDigit(c) => // ok
+        case c if c < 128 && Character.isLetter(c) => // ok
+        case _ => log.error("Invalid character in a preprocessor identifier", pos)
+      }
+      ident
+    }
+
     for (line <- lines) {
       lineNo += 1
       var resulting = ""
@@ -65,7 +77,13 @@ object Preprocessor {
                     log.warn(s"Undefined parameter $param, assuming 0", pos)
                     0L
                   })
-                case Array(p0,p1) => featureConstants += p0.trim() -> evalParam(p1, pos)
+                case Array(p0,p1) => featureConstants += assertIdentifier(p0.trim(), pos) -> evalParam(p1, pos)
+              }
+            }
+            case "define" => if (enabled) {
+              param.split("=", 2) match {
+                case Array(p0,p1) => currentFeatures += assertIdentifier(p0.trim(), pos) -> evalParam(p1, pos)
+                case _ => log.error("#define should have a parameter", pos)
               }
             }
             case "fatal" => if (enabled) log.fatal(param, pos)

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

@@ -214,6 +214,21 @@ class BasicSymonTest extends FunSuite with Matchers {
         | }
         | #endif
         |
+        | #if 1
+        | #define A=4
+        | #endif
+        | #if 0
+        | #define B=1
+        | #endif
+        |
+        | #if B
+        | #error B should not be defined
+        | #endif
+        |
+        | #if A != 4
+        | #error A should be defined
+        | #endif
+        |
         | #if 1 + 1 == 2
         |   #info 1
         |   #if      1 == 3