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2539e6af KR |
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 | // | |
425305df KR |
14 | private func READ(str: String) throws -> MalVal { |
15 | return try read_str(str) | |
2539e6af KR |
16 | } |
17 | ||
18 | // Walk the AST and completely evaluate it, handling macro expansions, special | |
19 | // forms and function calls. | |
20 | // | |
425305df | 21 | private func EVAL(ast: MalVal) -> MalVal { |
2539e6af KR |
22 | return ast |
23 | } | |
24 | ||
25 | // Convert the value into a human-readable string for printing. | |
26 | // | |
425305df | 27 | private func PRINT(exp: MalVal) -> String { |
2539e6af KR |
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 | // | |
425305df KR |
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 | } | |
2539e6af | 44 | } |
425305df | 45 | return nil |
2539e6af KR |
46 | } |
47 | ||
48 | // Perform the full READ/EVAL/PRINT, returning a printable string. | |
49 | // | |
425305df | 50 | private func REP(text: String) -> String? { |
2539e6af KR |
51 | let exp = RE(text) |
52 | if exp == nil { return nil } | |
53 | return PRINT(exp!) | |
54 | } | |
55 | ||
56 | // Perform the full REPL. | |
57 | // | |
425305df | 58 | private func REPL() { |
2539e6af KR |
59 | while true { |
60 | if let text = _readline("user> ") { | |
61 | if let output = REP(text) { | |
425305df | 62 | print("\(output)") |
2539e6af KR |
63 | } |
64 | } else { | |
425305df | 65 | print("") |
2539e6af KR |
66 | break |
67 | } | |
68 | } | |
69 | } | |
70 | ||
71 | func main() { | |
72 | load_history_file() | |
73 | REPL() | |
74 | save_history_file() | |
75 | } |