Use Boolean Values (#26)

src/commonMain/kotlin/com/github/fwilhe/inzell/StandardLibrary.kt

@@ -4,10 +4,25 @@ package com.github.fwilhe.inzell
 
 import kotlin.jvm.JvmName
 import kotlin.math.pow
+import kotlin.math.sqrt
 import kotlin.random.*
 
-fun isEven(x: Int): Double = if (x.rem(2) == 0) 1.0 else 0.0
-fun count(x: Int): Double = x.toDouble()
+fun isEven(x: Int): Boolean = x.rem(2) == 0
+
+fun isPrime(x: Int): Boolean {
+    if (x < 2) {
+        return false
+    }
+
+    for (i in 2..sqrt(x.toDouble()).toInt()){
+        if (x.rem(i) == 0) {
+            return false
+        }
+    }
+    return true
+}
+
+fun count(x: Int): Int = x
 
 fun sine(x: Int): Double = kotlin.math.sin(x.toDouble())
 fun cosine(x: Int): Double = kotlin.math.cos(x.toDouble())

src/commonTest/kotlin/SheetsTest.kt

@@ -13,6 +13,18 @@ class SheetsTest {
         assertEquals(expected, sheet)
     }
 
+    @Test
+    fun booleanValues() {
+        val sheet = spreadsheet {
+            column("i") { x -> count(x) }
+            column("is even") { x -> isEven(x) }
+            column("even and prime") { x -> isEven(x).and(isPrime(x)) }
+        }
+
+        MarkdownPrinter(sheet).printToStandardOut()
+
+    }
+
     @Test
     fun printTables() {
         val numberOfCpus = Column("Number of CPUs") { x -> x * x }

src/commonTest/kotlin/StandardLibraryTest.kt

@@ -0,0 +1,28 @@
+package com.github.fwilhe.inzell
+
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class StandardLibraryTest {
+    @Test
+    fun even() {
+        assertTrue(isEven(0))
+        assertFalse(isEven(1))
+        assertTrue(isEven(2))
+        assertFalse(isEven(3))
+    }
+
+    @Test
+    fun prime() {
+        assertFalse(isPrime(0))
+        assertFalse(isPrime(1))
+        assertTrue(isPrime(2))
+        assertTrue(isPrime(3))
+        assertFalse(isPrime(4))
+        assertTrue(isPrime(5))
+        assertFalse(isPrime(6))
+        assertTrue(isPrime(7))
+        assertFalse(isPrime(8))
+    }
+}