lib/mlton/basic/reader.sml

   1 (* Copyright (C) 2009 Matthew Fluet.
   2  * Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
   3  *    Jagannathan, and Stephen Weeks.
   4  *
   5  * MLton is released under a BSD-style license.
   6  * See the file MLton-LICENSE for details.
   7  *)
   8
   9 structure Reader: READER =
  10 struct
  11
  12 type ('a, 's) t = 's -> ('a * 's) option
  13
  14 fun char(r, c: char) s =
  15    case r s of
  16       NONE => NONE
  17     | SOME(c', s) => if c = c' then SOME((), s) else NONE
  18
  19 fun or rs s =
  20    let
  21       val rec loop =
  22          fn [] => NONE
  23           | r :: rs =>
  24                case r s of
  25                   NONE => loop rs
  26                 | z => z
  27    in loop rs
  28    end
  29
  30 fun all r s =
  31    let
  32       fun loop(s, ac) =
  33          case r s of
  34             NONE => SOME(rev ac, s)
  35           | SOME(x, s) => loop(s, x :: ac)
  36    in loop(s, [])
  37    end
  38
  39 fun firstN(r, n: Int.t) s =
  40    let
  41       fun loop(n, s, ac) =
  42          if n <= 0
  43             then SOME(rev ac, s)
  44          else (case r s of
  45                   NONE => NONE
  46                 | SOME(x, s) => loop(n - 1, s, x :: ac))
  47    in loop(n, s, [])
  48    end
  49
  50 fun mapFail(r, f) s =
  51    case r s of
  52       NONE => NONE
  53     | SOME(a, s) => Option.map(f a, fn b => (b, s))
  54
  55 fun map(r, f) = mapFail(r, SOME o f)
  56
  57 fun seq2(r1, r2) s =
  58    case r1 s of
  59       NONE => NONE
  60     | SOME(x1, s) =>
  61          case r2 s of
  62             NONE => NONE
  63           | SOME(x2, s) => SOME((x1, x2), s)
  64
  65
  66 fun seq3(r1, r2, r3) s =
  67    case r1 s of
  68       NONE => NONE
  69     | SOME(x1, s) =>
  70          case r2 s of
  71             NONE => NONE
  72           | SOME(x2, s) =>
  73                case r3 s of
  74                   NONE => NONE
  75                 | SOME(x3, s) => SOME((x1, x2, x3), s)
  76
  77 fun seq4(r1, r2, r3, r4) s =
  78    case seq3(r1, r2, r3) s of
  79       NONE => NONE
  80     | SOME((x1, x2, x3), s) =>
  81          case r4 s of
  82             NONE => NONE
  83           | SOME(x4, s) => SOME((x1, x2, x3, x4), s)
  84
  85 fun seq5(r1, r2, r3, r4, r5) s =
  86    case seq4(r1, r2, r3, r4) s of
  87       NONE => NONE
  88     | SOME((x1, x2, x3, x4), s) =>
  89          case r5 s of
  90             NONE => NONE
  91           | SOME(x5, s) => SOME((x1, x2, x3, x4, x5), s)
  92
  93 fun stringOfLength(r, i: Int.t) s =
  94    let
  95       fun loop(i, s, cs) =
  96          if i <= 0
  97             then SOME(implode(rev cs), s)
  98          else (case r s of
  99                   NONE => NONE
 100                 | SOME(c, s) => loop(i - 1, s, c :: cs))
 101    in loop(i, s, [])
 102    end
 103
 104 val info = Trace.info "Reader.readFromString"
 105
 106 fun readFromString(rm, s) =
 107    let val n: Int.t = String.size s
 108       fun reader(i: Int.t) =
 109          if i < n
 110             then SOME(String.sub(s, i), i + 1)
 111          else NONE
 112       val reader =
 113          Trace.traceInfo
 114          (info,
 115           Int.layout,
 116           fn NONE => Layout.str "NONE"
 117            | SOME(c, _) => Char.layout c,
 118           fn _ => (true, fn _ => true))
 119           reader
 120    in case rm reader (0: Int.t) of
 121       NONE => NONE
 122     | SOME(a, i) => if i = n then SOME a else NONE
 123    end
 124
 125 end