diff --git a/src/kiss/KissInterp.hx b/src/kiss/KissInterp.hx
index c8537f9..0df24bb 100644
--- a/src/kiss/KissInterp.hx
+++ b/src/kiss/KissInterp.hx
@@ -11,10 +11,14 @@ import kiss.Prelude;
  * macro definitions.
  */
 class KissInterp extends Interp {
+    var nullForUnknownVar:Bool;
+
     // TODO standardize this with KissConfig.prepareInterp
-    public function new() {
+    public function new(nullForUnknownVar = false) {
         super();
 
+        this.nullForUnknownVar = nullForUnknownVar;
+
         variables.set("Prelude", Prelude);
         variables.set("Lambda", Lambda);
         variables.set("Std", Std);
@@ -23,6 +27,18 @@ class KissInterp extends Interp {
         variables.set("Throw", ExtraElementHandling.Throw);
     }
 
+    override function resolve(id:String):Dynamic {
+        if (nullForUnknownVar) {
+            return try {
+                super.resolve(id);
+            } catch (e:Dynamic) {
+                null;
+            }
+        } else {
+            return super.resolve(id);
+        }
+    }
+
     override function exprReturn(e):Dynamic {
         // the default exprReturn() contains a try-catch which, though it is important, hides very important macroexpansion callstacks sometimes
         #if macrotest
diff --git a/src/kiss/Macros.hx b/src/kiss/Macros.hx
index eb85c0e..da8c5b0 100644
--- a/src/kiss/Macros.hx
+++ b/src/kiss/Macros.hx
@@ -8,6 +8,7 @@ import kiss.Kiss;
 import kiss.CompileError;
 import uuid.Uuid;
 import sys.io.Process;
+import hscript.Parser;
 
 using kiss.Kiss;
 using kiss.Reader;
@@ -171,6 +172,32 @@ class Macros {
                 ]);
         };
 
+        // Conditional compilation is all based on this macro:
+        macros["#if"] = (wholeExp:ReaderExp, exps:Array<ReaderExp>, k) -> {
+            wholeExp.checkNumArgs(2, 3, '(#if [cond] [then] [?else])');
+
+            var conditionExp = exps.shift();
+            var thenExp = exps.shift();
+            var elseExp = if (exps.length > 0) exps.shift(); else null;
+
+            var parser = new Parser();
+            var conditionInterp = new KissInterp(true);
+            var conditionStr = Reader.toString(conditionExp.def);
+            var conditionHScript = parser.parseString(Prelude.convertToHScript(conditionStr));
+            for (flag => value in Context.getDefines()) {
+                conditionInterp.variables.set(flag, value);
+            }
+            try {
+                return if (Prelude.truthy(conditionInterp.execute(conditionHScript))) {
+                    thenExp;
+                } else {
+                    elseExp;
+                }
+            } catch (e) {
+                throw CompileError.fromExp(conditionExp, 'condition for #if threw error $e');
+            }
+        };
+
         function bodyIf(formName:String, negated:Bool, wholeExp:ReaderExp, args:Array<ReaderExp>, k) {
             wholeExp.checkNumArgs(2, null, '($formName [condition] [body...])');
             var b = wholeExp.expBuilder();
diff --git a/src/kiss/Reader.hx b/src/kiss/Reader.hx
index 53473ca..da7c033 100644
--- a/src/kiss/Reader.hx
+++ b/src/kiss/Reader.hx
@@ -36,6 +36,16 @@ class Reader {
         readTable['"'] = readString;
         readTable["#"] = readRawString;
 
+        // Special symbols that wouldn't read as symbols, but should:
+        function forceSymbol(sym:String) {
+            readTable[sym] = (stream, k) -> Symbol(sym);
+        }
+        forceSymbol("#if");
+        forceSymbol("#when");
+        forceSymbol("#unless");
+        forceSymbol("#cond");
+        forceSymbol("#case");
+
         readTable["/*"] = (stream, k) -> {
             stream.takeUntilAndDrop("*/");
             null;
@@ -314,7 +324,7 @@ class Reader {
                 case '"':
                     break;
                 default:
-                    stream.error('Invalid syntax for raw string. Delete $next');
+                    stream.error('Invalid syntax for raw string.');
                     return null;
             }
         } while (true);
diff --git a/src/test/cases/ConditionalCompilationTestCase.hx b/src/test/cases/ConditionalCompilationTestCase.hx
new file mode 100644
index 0000000..a7d9c11
--- /dev/null
+++ b/src/test/cases/ConditionalCompilationTestCase.hx
@@ -0,0 +1,20 @@
+package test.cases;
+
+import utest.Assert;
+import utest.Test;
+import kiss.Prelude;
+
+@:build(kiss.Kiss.build())
+class ConditionalCompilationTestCase extends Test {
+    function testIf() {
+        #if interp
+        Assert.isTrue(runningInHaxe);
+        #else
+        Assert.isFalse(runningInHaxe);
+        #end
+
+        #if (py || js)
+        Assert.isTrue(runningInPyOrJs);
+        #end
+    }
+}
diff --git a/src/test/cases/ConditionalCompilationTestCase.kiss b/src/test/cases/ConditionalCompilationTestCase.kiss
new file mode 100644
index 0000000..8564fa2
--- /dev/null
+++ b/src/test/cases/ConditionalCompilationTestCase.kiss
@@ -0,0 +1,3 @@
+(defvar runningInHaxe (#if interp true false))
+(defvar runningInPyOrJs (#if (or py js) true false))
+