From 900c223ed40e36ffedce95e9a987d9a3c0309271 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Wed, 12 Apr 2017 16:47:45 +0200
Subject: Implementent conditional primitive

---
 repl.d           |  9 ++++++++-
 src/primitives.d | 27 +++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/repl.d b/repl.d
index 89c3104..4938a11 100644
--- a/repl.d
+++ b/repl.d
@@ -12,7 +12,14 @@ static import src.definition;
 static import src.primitives;
 
 void process(int x) {
-	stack.push(x);
+	try {
+		if ( !src.primitives.evaluate(x) ) {
+			stack.push(x);
+		}
+	}
+	catch (Exception ex) {
+		writeln("Error: ", ex.msg);
+	}
 }
 
 void process(string word) {
diff --git a/src/primitives.d b/src/primitives.d
index 0be6836..f577713 100644
--- a/src/primitives.d
+++ b/src/primitives.d
@@ -6,8 +6,21 @@ import src.stack;
 import src.definition;
 
 int[string] variables;
+bool        drop_mode;
+
+bool evaluate(int value) {
+	return drop_mode;
+}
 
 bool evaluate(string word) {
+	if ( drop_mode ) {
+		if ( word == "then" ) {
+			drop_mode = false;
+		}
+
+		return true;
+	}
+
 	switch ( word ) {
 		case "§":
 			src.definition.start;
@@ -25,6 +38,20 @@ bool evaluate(string word) {
 				stack.push(variables[name]);
 			}
 			return true;
+		case "if":
+			switch ( stack.pop.get!int ) {
+				case 0:
+					drop_mode = true;
+					return true;
+				case 1:
+					drop_mode = false;
+					return true;
+				default:
+					throw new Exception("invalid logic value");
+			}
+		case "then":
+			drop_mode = false;
+			return true;
 		case "+":
 			int b = stack.pop.get!int;
 			int a = stack.pop.get!int;
-- 
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