NimYAML/private/hints.nim

#            NimYAML - YAML implementation in Nim
#        (c) Copyright 2015 Felix Krause
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.

type
    YamlTypeHintState = enum
        ythInitial,
        ythF, ythFA, ythFAL, ythFALS, ythFALSE,
        ythN, ythNU, ythNUL, ythNULL,
              ythNO,
        ythO, ythON,
              ythOF, ythOFF,
        ythT, ythTR, ythTRU, ythTRUE,
        ythY, ythYE, ythYES,
        
        ythPoint, ythPointI, ythPointIN, ythPointINF,
                  ythPointN, ythPointNA, ythPointNAN,
        
        ythLowerFA, ythLowerFAL, ythLowerFALS,
        ythLowerNU, ythLowerNUL,
        ythLowerOF,
        ythLowerTR, ythLowerTRU,
        ythLowerYE,
                
        ythPointLowerIN, ythPointLowerN, ythPointLowerNA,
        
        ythMinus, yth0, ythInt, ythDecimal, ythNumE, ythNumEPlusMinus,
        ythExponent

macro typeHintStateMachine(c: untyped, content: untyped): stmt =
    assert content.kind == nnkStmtList
    result = newNimNode(nnkCaseStmt, content).add(copyNimNode(c))
    for branch in content.children:
        assert branch.kind == nnkOfBranch
        var 
            charBranch = newNimNode(nnkOfBranch, branch)
            i = 0
            stateBranches = newNimNode(nnkCaseStmt, branch).add(
                    newIdentNode("typeHintState"))
        while branch[i].kind != nnkStmtList:
            charBranch.add(copyNimTree(branch[i]))
            inc(i)
        for rule in branch[i].children:
            assert rule.kind == nnkInfix
            assert ($rule[0].ident == "=>")
            var stateBranch = newNimNode(nnkOfBranch, rule)
            case rule[1].kind
            of nnkBracket:
                for item in rule[1].children: stateBranch.add(item)
            of nnkIdent: stateBranch.add(rule[1])
            else: assert false
            if rule[2].kind == nnkNilLit:
                stateBranch.add(newStmtList(newNimNode(nnkDiscardStmt).add(
                        newEmptyNode())))
            else:
                stateBranch.add(newStmtList(newAssignment(
                        newIdentNode("typeHintState"), copyNimTree(rule[2]))))
            stateBranches.add(stateBranch)
        stateBranches.add(newNimNode(nnkElse).add(newStmtList(
                newNimNode(nnkReturnStmt).add(newIdentNode("yTypeUnknown")))))
        charBranch.add(newStmtList(stateBranches))
        result.add(charBranch)
    result.add(newNimNode(nnkElse).add(newStmtList(
            newNimNode(nnkReturnStmt).add(newIdentNode("yTypeUnknown")))))

template advanceTypeHint(ch: char) {.dirty.} =
    typeHintStateMachine ch:
    of '~': ythInitial => ythNULL
    of '.':
        [yth0, ythInt]         => ythDecimal
        [ythInitial, ythMinus] => ythPoint
    of '+': ythNumE => ythNumEPlusMinus
    of '-':
        ythInitial => ythMinus
        ythNumE    => ythNumEPlusMinus
    of '0':
        [ythInitial, ythMinus]      => yth0
        [ythNumE, ythNumEPlusMinus] => ythExponent
    of '1'..'9':
        [ythInitial, ythMinus]            => ythInt
        [ythNumE, ythNumEPlusMinus]       => ythExponent
        [ythInt, ythDecimal, ythExponent] => nil
    of 'a':
        ythF           => ythLowerFA
        ythPointN      => ythPointNA
        ythPointLowerN => ythPointLowerNA
    of 'A':
        ythF      => ythFA
        ythPointN => ythPointNA
    of 'e':
        [yth0, ythInt, ythDecimal] => ythNumE
        ythLowerFALS => ythFALSE
        ythLowerTRU  => ythTRUE
        ythY         => ythLowerYE
    of 'E':
        [yth0, ythInt, ythDecimal] => ythNumE
        ythFALS => ythFALSE
        ythTRU  => ythTRUE
        ythY    => ythYE
    of 'f':
        ythInitial      => ythF
        ythO            => ythLowerOF
        ythLowerOF      => ythOFF
        ythPointLowerIN => ythPointINF
    of 'F':
        ythInitial => ythF
        ythO       => ythOF
        ythOF      => ythOFF
        ythPointIN => ythPointINF
    of 'i', 'I': ythPoint => ythPointI
    of 'l':
        ythLowerNU  => ythLowerNUL
        ythLowerNUL => ythNULL
        ythLowerFA  => ythLowerFAL
    of 'L':
        ythNU  => ythNUL
        ythNUL => ythNULL
        ythFA  => ythFAL
    of 'n':
        ythInitial      => ythN
        ythO            => ythON
        ythPoint        => ythPointLowerN
        ythPointI       => ythPointLowerIN
        ythPointLowerNA => ythPointNAN
    of 'N':
        ythInitial => ythN
        ythO       => ythON
        ythPoint   => ythPointN
        ythPointI  => ythPointIN
        ythPointNA => ythPointNAN
    of 'o', 'O':
        ythInitial => ythO
        ythN       => ythNO
    of 'r': ythT => ythLowerTR
    of 'R': ythT => ythTR
    of 's':
        ythLowerFAL => ythLowerFALS
        ythLowerYE  => ythYES
    of 'S':
        ythFAL => ythFALS
        ythYE  => ythYES
    of 't', 'T': ythInitial => ythT
    of 'u':
        ythN       => ythLowerNU
        ythLowerTR => ythLowerTRU
    of 'U':
        ythN  => ythNU
        ythTR => ythTRU
    of 'y', 'Y': ythInitial => ythY

proc guessType*(scalar: string): TypeHint =
    var typeHintState: YamlTypeHintState = ythInitial
    for c in scalar: advanceTypeHint(c)
    case typeHintState
    of ythNULL: result = yTypeNull
    of ythTRUE, ythON, ythYES, ythY: result = yTypeBoolTrue
    of ythFALSE, ythOFF, ythNO, ythN: result = yTypeBoolFalse
    of ythInt, yth0: result = yTypeInteger
    of ythDecimal, ythExponent: result = yTypeFloat
    of ythPointINF: result = yTypeFloatInf
    of ythPointNAN: result = yTypeFloatNaN
    else: result = yTypeUnknown