Minor fixes

Add '%' operation (accidentally omitted)
Add strMode function to properly handle String mode (broken before)
Change null checks to use null say let
Add peek function to handle peeking an empty stack (returns 0)
Fix '\' operation (broken, did not swap top 2 stack elements)
Add temporary output handling for testing
Add temporary input handling for testing
Add '0' - '9' operations (unintentionally omitted before)
Fix skipping spaces while in String mode
Step returns whether pointer is inactive or not; whether the program has terminated

befunge/src/main/kotlin/befide/befunge/b93/B93Interpreter.kt

@@ -33,10 +33,11 @@ class B93Interpreter : Interpreter {
 
     private fun pop(): Value {
         val v = _pop()
-        if (v != null) {
-            stackChanged(StackEvent(StackAction.Pop, listOf(v)))
-        }
-        return Value(0)
+        val ret = v?.let {
+            stackChanged(StackEvent(StackAction.Pop, listOf(it)))
+            it
+        } ?: Value(0)
+        return ret
     }
 
     private fun pop(num: Int): List<Value> {
@@ -59,6 +60,13 @@ class B93Interpreter : Interpreter {
         stackChanged.invoke(StackEvent(StackAction.Push, vs))
     }
 
+    private fun peek(): Value {
+        if (!stack.empty()) {
+            return stack.peek()
+        }
+        return Value(0)
+    }
+
     private fun binop(bop: Char) {
         val (vb, va) = pop(2)
         val a = va.value
@@ -68,10 +76,11 @@ class B93Interpreter : Interpreter {
             '-' -> a - b
             '*' -> a * b
             '/' -> a / b
+            '%' -> a % b
             '`' -> if (a > b) 1L else 0L
             else -> null
         }
-        if (res != null) {
+        res?.let {
             val vres = Value(res)
             push(vres)
         }
@@ -84,8 +93,8 @@ class B93Interpreter : Interpreter {
             '!' -> if (v == 0L) 1L else 0L
             else -> null
         }
-        if (res != null) {
-            val vres = Value(res)
+        res?.let {
+            val vres = Value(it)
             push(vres)
         }
     }
@@ -98,8 +107,8 @@ class B93Interpreter : Interpreter {
             'v' -> DOWN
             else -> null
         }
-        if (newDelta != null) {
-            ip.delta = newDelta
+        newDelta?.let {
+            ip.delta = it
         }
     }
 
@@ -117,8 +126,8 @@ class B93Interpreter : Interpreter {
             '_' -> if (cond) RIGHT else LEFT
             else -> null
         }
-        if (newDelta != null) {
-            ip.delta = newDelta
+        newDelta?.let {
+            ip.delta = it
         }
     }
 
@@ -134,12 +143,12 @@ class B93Interpreter : Interpreter {
     private fun stackop(sop: Char) {
         when (sop) {
             ':' -> {
-                val vc = stack.peek().copy()
+                val vc = peek().copy()
                 push(vc)
             }
             '\\' -> {
                 val (v2, v1) = pop(2)
-                push(listOf(v1, v2))
+                push(listOf(v2, v1))
             }
             '$' -> {
                 pop()
@@ -151,10 +160,11 @@ class B93Interpreter : Interpreter {
         val vv = pop()
         val v = vv.value
         val out = when (type) {
-            '.' -> v.toString().toCharArray()
+            '.' -> v.toString().toCharArray() + ' '
             ',' -> charArrayOf(v.toChar())
             else -> charArrayOf()
         }
+        print(out) //TEMPORARY
         //TODO output {out} chararray
     }
 
@@ -163,9 +173,13 @@ class B93Interpreter : Interpreter {
         // No ipChanged here, shown in execInstr
     }
 
-    private fun input() {
-        val inp = 0L //TODO get input
-        val vinp = Value(inp)
+    private fun input(type: Char) {
+        val inp = readLine()
+        val vinp = Value(when(type) {
+            '&' -> inp?.toLong() ?: 0L
+            '~' -> inp?.get(0)?.toLong() ?: 0L
+            else -> 0L
+        })
         push(vinp)
     }
 
@@ -198,6 +212,11 @@ class B93Interpreter : Interpreter {
         ip.mode = IpMode.Inactive
     }
 
+    private fun pushDig(dig: Char) {
+        val num = dig.toLong() - '0'.toLong()
+        push(Value(num))
+    }
+
     private fun noOp() {}
 
     private fun execInstr(instr: Value) {
@@ -215,29 +234,40 @@ class B93Interpreter : Interpreter {
             '#' -> stepIP()
             'g' -> fget()
             'p' -> fput()
-            '&', '~' -> input()
+            '&', '~' -> input(car)
             '@' -> terminate()
+            in '0'..'9' -> pushDig(car)
             else -> noOp()
         }
     }
 
+    private fun strMode(instr: Value) {
+        if (instr.asChar == '"') {
+            toggleStrmode()
+            return
+        }
+        push(instr)
+    }
+
     override fun step(): Boolean {
         val instr = funge[ip.pos]
         val currIP = ip.copy()
         when (ip.mode) {
             IpMode.Inactive -> noOp()
             IpMode.Normal -> execInstr(instr)
-            IpMode.String -> push(instr)
+            IpMode.String -> strMode(instr)
         }
         if (ip.mode != IpMode.Inactive) {
             stepIP()
-            while (funge[ip.pos].asChar == ' ') {
-                stepIP()
+            if (ip.mode != IpMode.String) {
+                while (funge[ip.pos].asChar == ' ') {
+                    stepIP()
+                }
             }
             val newIP = ip.copy()
             ipChanged(IpEvent(currIP, newIP))
         }
-        return true
+        return ip.mode != IpMode.Inactive
     }
 
     override fun reset() {