fix #80 edge case !isSomething() bug fixed

+String.last()

docs/tutorial.md

@@ -1385,6 +1385,7 @@ Typical set of String functions includes:
 | trim()             | trim space chars from both ends                            |
 | startsWith(prefix) | true if starts with a prefix                               |
 | endsWith(prefix)   | true if ends with a prefix                                 |
+| last()             | get last character of a string or throw                    |
 | take(n)            | get a new string from up to n first characters             |
 | takeLast(n)        | get a new string from up to n last characters              |
 | drop(n)            | get a new string dropping n first chars, or empty string   |

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Parser.kt

@@ -213,25 +213,40 @@ private class Parser(fromPos: Pos) {
 
             '!' -> {
                 if (currentChar == 'i') {
+                    // Potentially !in / !is, but only if a word boundary follows
                     pos.advance()
                     when (currentChar) {
                         'n' -> {
                             pos.advance()
+                            // if next char continues an identifier, it's actually '!'+identifier starting with "in..."
+                            if (idNextChars(currentChar)) {
+                                // backtrack to right after '!'
+                                pos.back()
+                                pos.back()
+                                Token("!", from, Token.Type.NOT)
+                            } else
                                 Token("!in", from, Token.Type.NOTIN)
                         }
 
                         's' -> {
                             pos.advance()
+                            // if next char continues an identifier, it's actually '!'+identifier starting with "is..."
+                            if (idNextChars(currentChar)) {
+                                // backtrack to right after '!'
+                                pos.back()
+                                pos.back()
+                                Token("!", from, Token.Type.NOT)
+                            } else
                                 Token("!is", from, Token.Type.NOTIS)
                         }
 
                         else -> {
+                            // it was just '!i' followed by something else; revert one step and return '!'
                             pos.back()
                             Token("!", from, Token.Type.NOT)
                         }
                     }
-                } else
+                } else if (currentChar == '=') {
-                    if (currentChar == '=') {
                         pos.advance()
                         if (currentChar == '=') {
                             pos.advance()

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjString.kt

@@ -173,6 +173,9 @@ data class ObjString(val value: String) : Obj() {
                     thisAs<ObjString>().value.map { ObjChar(it) }.toMutableList()
                 )
             }
+            addFn("last") {
+                ObjChar(thisAs<ObjString>().value.lastOrNull() ?: raiseNoSuchElement("empty string"))
+            }
             addFn("encodeUtf8") { ObjBuffer(thisAs<ObjString>().value.encodeToByteArray().asUByteArray()) }
             addFn("size") { ObjInt(thisAs<ObjString>().value.length.toLong()) }
             addFn("toReal") {

lynglib/src/commonTest/kotlin/ScriptTest.kt

@@ -4012,4 +4012,41 @@ class ScriptTest {
         """.trimIndent()).decodeSerializable<TestJson4>()
         assertEquals( TestJson4(TestEnum.One), x)
     }
+
+    @Test
+    fun testLogicalNot() = runTest {
+        eval("""
+            val vf = false 
+            fun f() { false }
+            assert( !false )
+            assert( !vf )
+            assert( !f() )
+            
+            val vt = true
+            fun ft() { true }
+            if( !true )
+                throw "impossible"
+                
+            if( !ft() )
+                throw "impossible"
+                
+            if( !vt )
+                throw "impossible"
+                
+            // real world sample
+
+            fun isSignedByAdmin() {
+                // just ok
+                true
+            }
+            
+            fun requireAdmin() {
+                // this caused compilation error:
+                if( !isSignedByAdmin() )
+                    throw "Admin signature required"
+            }
+        
+        """.trimIndent()
+        )
+    }
 }