June 2018 Update

Task/S-Expressions/Kotlin/s-expressions.kotlin

@@ -0,0 +1,98 @@
+// version 1.2.31
+
+const val INDENT = 2
+
+fun String.parseSExpr(): List<String>? {
+    val r = Regex("""\s*("[^"]*"|\(|\)|"|[^\s()"]+)""")
+    val t = r.findAll(this).map { it.value }.toMutableList()
+    if (t.size == 0) return null
+    var o = false
+    var c = 0
+    for (i in t.size - 1 downTo 0) {
+        val ti = t[i].trim()
+        val nd = ti.toDoubleOrNull()
+        if (ti == "\"") return null
+        if (ti == "(") {
+            t[i] = "["
+            c++
+        }
+        else if (ti == ")") {
+            t[i] = "]"
+            c--
+        }
+        else if (nd != null) {
+             val ni = ti.toIntOrNull()
+             if (ni != null) t[i] = ni.toString()
+             else t[i] = nd.toString()
+        }
+        else if (ti.startsWith("\"")) { // escape embedded double quotes
+             var temp = ti.drop(1).dropLast(1)
+             t[i] = "\"" + temp.replace("\"", "\\\"") + "\""
+        }
+        if (i > 0 && t[i] != "]" && t[i - 1].trim() != "(") t.add(i, ", ")
+        if (c == 0) {
+            if (!o) o = true else return null
+        }
+    }
+    return if (c != 0) null else t
+}
+
+fun MutableList<String>.toSExpr(): String {
+    for (i in 0 until this.size) {
+        this[i] = when (this[i]) {
+            "["  -> "("
+            "]"  -> ")"
+            ", " -> " "
+            else ->  {
+                if (this[i].startsWith("\"")) { // unescape embedded quotes
+                    var temp = this[i].drop(1).dropLast(1)
+                    "\"" + temp.replace("\\\"", "\"") + "\""
+                }
+                else this[i]
+            }
+        }
+    }
+    return this.joinToString("")
+}
+
+fun List<String>.prettyPrint() {
+    var level = 0
+    loop@for (t in this) {
+        var n: Int
+        when(t) {
+            ", ", " " -> continue@loop
+            "[", "(" -> {
+                n = level * INDENT + 1
+                level++
+             }
+             "]", ")" -> {
+                level--
+                n = level * INDENT + 1
+             }
+             else -> {
+                n = level * INDENT + t.length
+             }
+        }
+        println("%${n}s".format(t))
+    }
+}
+
+fun main(args: Array<String>) {
+    val str = """((data "quoted data" 123 4.5)""" + "\n" +
+              """ (data (!@# (4.5) "(more" "data)")))"""
+    val tokens = str.parseSExpr()
+    if (tokens == null)
+        println("Invalid s-expr!")
+    else {
+        println("Native data structure:")
+        println(tokens.joinToString(""))
+        println("\nNative data structure (pretty print):")
+        tokens.prettyPrint()
+
+        val tokens2 = tokens.toMutableList()
+        println("\nRecovered S-Expression:")
+        println(tokens2.toSExpr())
+        println("\nRecovered S-Expression (pretty print):")
+        tokens2.prettyPrint()
+    }
+}