Preprocessor: add #use A=B and if(i,t,e)

CHANGELOG.md

@@ -44,6 +44,10 @@
 
 * 6502: Fixed optimizations of comparisons.
 
+* Preprocessor: Added `#use A=B` directive
+
+* Preprocessor: Added `if` function
+
 * Fixed volatile-related bugs.
 
 * Fixed optimizations removing jumps to jumps.

docs/lang/preprocessor.md

@@ -103,7 +103,14 @@ The following features are defined based on the chosen CPU and compilation optio
 The `defined` function returns 1 if the feature is defined, 0 otherwise.  
 All the other functions and operators treat undefined features as if they were defined as 0. 
 
-TODO
+The `if` function returns its second parameter if the first parameter is defined and non-zero, and the third parameter otherwise:
+
+    // prints 400:
+    #infoeval if(1, 400, 500)
+    // prints 500:
+    #infoeval if(0, 400, 500)
+
+TODO   
 `not`, `lo`, `hi`, `+`, `-`, `*`, `|`, `&`, `^`, `||`, `&&`, `<<`, `>>`,`==`, `!=`, `>`, `>=`, `<`, `<=`
 
 The following Millfork operators and functions are not available in the preprocessor:  
@@ -140,11 +147,22 @@ Evaluates an expression and emits the result as a diagnostic message.
 
 ### `#use`
 
-Exports a feature value under its name to the parser.
-The parser will substitute every use of that name as a variable or constant 
+    #use <ident> = <expr>
+    
+    #use <feature>
+    // equivalent to #use <feature> = <feature>
+
+Exports a value to the parser.
+The parser will substitute every use of the given identifier as a variable or constant 
 with the numeric value of the feature.
+
+    #use CPU_MODEL = if(CPU_65816 | ARCH_X86, 16, 8)
+    putstrz("Your CPU is "z)
+    putword(CPU_MODEL)
+    putstrz("-bit."z)
+
 The substitution will happen only within the current file.
-To use such value in other files, consider this:
+To use such value in other files, consider using a normal constant:
 
     #use WIDESCREEN
     const byte is_widescreen = WIDESCREEN

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

@@ -59,10 +59,14 @@ object Preprocessor {
           keyword match {
             case "use" => if (enabled) {
               if (param == "") log.error("#use should have a parameter", pos)
-              featureConstants += param -> options.features.getOrElse(param, {
-                log.warn(s"Undefined parameter $param, assuming 0", pos)
-                0L
-              })
+              param.split("=", 2) match {
+                case Array(p) =>
+                  featureConstants += param -> options.features.getOrElse(param, {
+                    log.warn(s"Undefined parameter $param, assuming 0", pos)
+                    0L
+                  })
+                case Array(p0,p1) => featureConstants += p0.trim() -> evalParam(p1, pos)
+              }
             }
             case "fatal" => if (enabled) log.fatal(param, pos)
             case "error" => if (enabled) log.error(param, pos)
@@ -167,7 +171,8 @@ class PreprocessorParser(options: CompilationOptions) {
     case ("not", List(p)) => {m:M => Some(if (p(m).getOrElse(0L) == 0) 1 else 0)}
     case ("lo", List(p)) => {m:M => Some(p(m).getOrElse(0L) & 0xff)}
     case ("hi", List(p)) => {m:M => Some(p(m).getOrElse(0L).>>(8).&(0xff))}
-    case ("defined" | "lo" | "hi" | "not", ps) =>
+    case ("if", List(i, t, e)) => {m:M => if (i(m).getOrElse(0L) != 0) t(m) else e(m)}
+    case ("defined" | "lo" | "hi" | "not" | "if", ps) =>
       log.error(s"Invalid number of parameters to $name: ${ps.length}")
       alwaysNone
     case _ =>

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

@@ -195,14 +195,17 @@ class BasicSymonTest extends FunSuite with Matchers {
         | #use ARCH_6502
         | #use ARCH_I80
         |
+        | #use HORSE = ARCH_6502
+        | #use COW = ARCH_I80
+        |
         | #if 1
         | asm void main () {
         |   #if ARCH_6502
-        |     lda #ARCH_6502
+        |     lda #HORSE
         |     sta output
         |     rts
         |   #elseif ARCH_I80
-        |     ld a,ARCH_I80
+        |     ld a,COW
         |     ld (output),a
         |     ret
         |   #else