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Decision tables: Difference between revisions
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Check the printer-computer cable
Ensure printer software is installed</pre>
=={{header|Nim}}==
We have defined a generic decision table object and used it with the Wikipedia printer example.
<lang Nim>import strutils, tables
####################################################################################################
# Generic defintion of the decision table.
type
DTable[Cond, Act: Ordinal] = object
questions: array[Cond, string]
answers: array[Act, string]
rules: Table[set[Cond], seq[Act]]
proc initDTable[Cond, Act](): DTable[Cond, Act] = discard
proc addCondition[Cond, Act](dt: var DTable[Cond, Act]; cond: Cond; question: string) =
if dt.questions[cond].len != 0:
raise newException(ValueError, "condition already set: " & $cond)
dt.questions[cond] = question
proc addAction[Cond, Act](dt: var DTable[Cond, Act]; act: Act; answer: string) =
if dt.answers[act].len != 0:
raise newException(ValueError, "action already set: " & $act)
dt.answers[act] = answer
proc addRule[Cond, Act](dt: var DTable[Cond, Act]; rule: set[Cond]; acts: openArray[Act]) =
if rule in dt.rules:
raise newException(ValueError, "rule already set.")
dt.rules[rule] = @acts
proc askQuestion(question: string): string =
while true:
stdout.write question & ' '
stdout.flushFile()
result = stdin.readLine().strip()
if result in ["y", "n"]: break
proc apply[Cond, Act](dt: DTable[Cond, Act]) =
# Build condition set.
var conds: set[Cond]
echo "Answer questions with 'y' or 'n'"
for cond, question in dt.questions:
if question.len == 0:
raise newException(ValueError, "missing question for condition: " & $cond)
let answer = askQuestion(question)
if answer == "y":
conds.incl cond
# Apply rule.
echo()
if conds in dt.rules:
echo "Actions recommended:"
for act in dt.rules[conds]:
echo "- ", dt.answers[act]
else:
echo "No action recommended."
####################################################################################################
# Decision table for Wikipedia printer example.
type
Condition {.pure.} = enum PrinterPrints, RedLightFlashing, PrinterRecognized
Action {.pure.} = enum CheckPowerCable, CheckPrinterCable, CheckSoftware, CheckInk, CheckPaperJam
const
Questions = [PrinterPrints: "Does printer print?",
RedLightFlashing: "Does red light is flashing?",
PrinterRecognized: "Is printer recognized by computer?"]
Answers = [CheckPowerCable: "check the power cable",
CheckPrinterCable: "check the printer-computer cable",
CheckSoftware: "ensure printer software is installed",
CheckInk: "check/replace ink",
CheckPaperJam: "check for paper jam"]
var dt = initDTable[Condition, Action]()
for cond, question in Questions:
dt.addCondition(cond, question)
for act, answer in Answers:
dt.addAction(act, answer)
dt.addRule({}, [CheckPowerCable, CheckPrinterCable, CheckSoftware])
dt.addRule({PrinterPrints}, [CheckSoftware])
dt.addRule({RedLightFlashing}, [CheckPrinterCable, CheckSoftware, CheckInk])
dt.addRule({PrinterRecognized}, [CheckPaperJam])
dt.addRule({PrinterPrints, RedLightFlashing}, [CheckSoftware])
dt.addRule({RedLightFlashing, PrinterRecognized}, [CheckInk, CheckPaperJam])
dt.addRule({PrinterPrints, RedLightFlashing, PrinterRecognized}, [CheckInk])
dt.apply()</lang>
{{out}}
<pre>Answer questions with 'y' or 'n'
Does printer print? n
Does red light is flashing? y
Is printer recognized by computer? y
Actions recommended:
- check/replace ink
- check for paper jam</pre>
=={{header|Perl}}==
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