✨ adding a way to print the expression in LISP style

Author: igorkulman

PascalInterpreter.playground/Contents.swift

@@ -21,3 +21,6 @@ print(parser.expr())
 
 let rpn = RPN("(5 + 3) * 12 / 3")
 rpn.eval()
+
+let ln = LISPNotation("(2 + 3 * 5)")
+ln.eval()

SwiftPascalInterpreter/SwiftPascalInterpreter/Extensions.swift

@@ -97,6 +97,24 @@ extension Interpreter: CustomStringConvertible {
     }
 }
 
+extension Parser: CustomStringConvertible {
+    public var description: String {
+        return "Parser"
+    }
+}
+
+extension RPN: CustomStringConvertible {
+    public var description: String {
+        return "Reverse polish notation"
+    }
+}
+
+extension LISPNotation: CustomStringConvertible {
+    public var description: String {
+        return "LISP notation"
+    }
+}
+
 extension AST: CustomStringConvertible {
     public var description: String {
         return treeString(self, using: { node in

SwiftPascalInterpreter/SwiftPascalInterpreter/Notations.swift

@@ -8,10 +8,14 @@
 
 import Foundation
 
+public protocol Notation {
+    func eval() -> String
+}
+
 /**
  Reverse polish notation
  */
-public class RPN {
+public class RPN: Notation {
     private let parser: Parser
 
     public init(_ text: String) {
@@ -32,3 +36,28 @@ public class RPN {
         }
     }
 }
+
+/**
+ LISP notation
+ */
+public class LISPNotation: Notation {
+    private let parser: Parser
+
+    public init(_ text: String) {
+        parser = Parser(text)
+    }
+
+    public func eval() -> String {
+        let node = parser.expr()
+        return visit(node)
+    }
+
+    private func visit(_ node: AST) -> String {
+        switch node {
+        case let .number(value):
+            return "\(value)"
+        case let .binaryOperation(left: left, operation: operation, right: right):
+            return "(\(operation.shortDescription) \(visit(left)) \(visit(right)))"
+        }
+    }
+}