Data commit

Task/Truth-table/Kotlin/truth-table.kotlin

@@ -0,0 +1,74 @@
+// Version 1.2.31
+
+import java.util.Stack
+
+class Variable(val name: Char, var value: Boolean = false)
+
+lateinit var expr: String
+var variables = mutableListOf<Variable>()
+
+fun Char.isOperator() = this in "&|!^"
+
+fun Char.isVariable() = this in variables.map { it.name }
+
+fun evalExpression(): Boolean {
+    val stack = Stack<Boolean>()
+
+    for (e in expr) {
+        stack.push(
+            if (e == 'T')
+                true
+            else if (e == 'F')
+                false
+            else if (e.isVariable())
+                variables.single { it.name == e }.value
+            else when (e) {
+                '&'   -> stack.pop() and stack.pop()
+                '|'   -> stack.pop() or  stack.pop()
+                '!'   -> !stack.pop()
+                '^'   -> stack.pop() xor stack.pop()
+                else  -> throw RuntimeException("Non-conformant character '$e' in expression")
+            }
+        )
+    }
+
+    require(stack.size == 1)
+    return stack.peek()
+}
+
+fun setVariables(pos: Int) {
+    require(pos <= variables.size)
+    if (pos == variables.size) {
+        val vs = variables.map { if (it.value) "T" else "F" }.joinToString("  ")
+        val es = if (evalExpression()) "T" else "F"
+        return println("$vs  $es")
+    }
+    variables[pos].value = false
+    setVariables(pos + 1)
+    variables[pos].value = true
+    setVariables(pos + 1)
+}
+
+fun main(args: Array<String>) {
+    println("Accepts single-character variables (except for 'T' and 'F',")
+    println("which specify explicit true or false values), postfix, with")
+    println("&|!^ for and, or, not, xor, respectively; optionally")
+    println("seperated by spaces or tabs. Just enter nothing to quit.")
+
+    while (true) {
+        print("\nBoolean expression: ")
+        expr = readLine()!!.toUpperCase().replace(" ", "").replace("\t", "")
+        if (expr == "") return
+        variables.clear()
+        for (e in expr) {
+            if (!e.isOperator() && e !in "TF" && !e.isVariable()) variables.add(Variable(e))
+        }
+        if (variables.isEmpty()) return
+        val vs = variables.map { it.name }.joinToString("  ")
+        println("\n$vs  $expr")
+        val h = vs.length + expr.length + 2
+        repeat(h) { print("=") }
+        println("\n")
+        setVariables(0)
+    }
+}