swift/step1_read_print.swift

   1 //******************************************************************************
   2 // MAL - step 1 - read/print
   3 //******************************************************************************
   4 // This file is automatically generated from templates/step.swift. Rather than
   5 // editing it directly, it's probably better to edit templates/step.swift and
   6 // regenerate this file. Otherwise, your change might be lost if/when someone
   7 // else performs that process.
   8 //******************************************************************************
   9
  10 import Foundation
  11
  12 // Parse the string into an AST.
  13 //
  14 private func READ(str: String) throws -> MalVal {
  15     return try read_str(str)
  16 }
  17
  18 // Walk the AST and completely evaluate it, handling macro expansions, special
  19 // forms and function calls.
  20 //
  21 private func EVAL(ast: MalVal) -> MalVal {
  22     return ast
  23 }
  24
  25 // Convert the value into a human-readable string for printing.
  26 //
  27 private func PRINT(exp: MalVal) -> String {
  28     return pr_str(exp, true)
  29 }
  30
  31 // Perform the READ and EVAL steps. Useful for when you don't care about the
  32 // printable result.
  33 //
  34 private func RE(text: String) -> MalVal? {
  35     if !text.isEmpty {
  36         do {
  37             let ast = try READ(text)
  38                 return EVAL(ast)
  39         } catch let error as MalException {
  40             print("Error parsing input: \(error)")
  41         } catch {
  42             print("Error parsing input: \(error)")
  43         }
  44     }
  45     return nil
  46 }
  47
  48 // Perform the full READ/EVAL/PRINT, returning a printable string.
  49 //
  50 private func REP(text: String) -> String? {
  51     let exp = RE(text)
  52     if exp == nil { return nil }
  53     return PRINT(exp!)
  54 }
  55
  56 // Perform the full REPL.
  57 //
  58 private func REPL() {
  59     while true {
  60         if let text = _readline("user> ") {
  61             if let output = REP(text) {
  62                 print("\(output)")
  63             }
  64         } else {
  65             print("")
  66             break
  67         }
  68     }
  69 }
  70
  71 func main() {
  72     load_history_file()
  73     REPL()
  74     save_history_file()
  75 }