[rust] Bob

1 files changed, 75 insertions, 0 deletions

diff --git a/bob/src/lib.rs b/bob/src/lib.rs
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+/* The solution consists of an implementation of a simple Finite State Automaton whose states and
+ * transition messages are represented by the `State` and `Message` enums.
+ *
+ * `process(State, Message) -> State` represents the main transition function for the FSA. This
+ * allows us to compute the answer with a single visit of the input string.
+ *
+ * Note: some duplicate states (`QuestLow`, `ElseLow`) are needed in order to remember whether we
+ * have seen a lowercase character already or not. This is probably not the minimal number of
+ * states required to solve the problem.
+ */
+enum State { Nothing, QuestLow, Quest, Yell, YellQ, ElseLow, Else }
+enum Message { Whitespace, Upper, Lower, Symbol, Question }
+
+fn to_message(c: char) -> Message {
+    match c as u8 {
+        0..=32   => Message::Whitespace,    // All controll characters are considered whitespace
+        63       => Message::Question,
+        65..=90  => Message::Upper,
+        97..=122 => Message::Lower,
+        _        => Message::Symbol         // Anything else (numbers incl.) is a symbol
+    }
+}
+
+fn process(s: State, m: Message) -> State {
+    match s {
+        State::Nothing => match m {
+            Message::Whitespace => s,
+            Message::Upper => State::Yell,
+            Message::Lower => State::ElseLow,
+            Message::Question => State::Quest,
+            Message::Symbol => State::Else
+        },
+        State::QuestLow => match m {
+            Message::Whitespace | Message::Question => s,
+            _ => State::ElseLow
+        },
+        State::Quest => match m {
+            Message::Upper => State::Yell,
+            Message::Lower => State::ElseLow,
+            Message::Symbol => State::Else,
+            _ => s
+        },
+        State::Yell => match m {
+            Message::Lower => State::ElseLow,
+            Message::Question => State::YellQ,
+            _ => s
+        },
+        State::YellQ => match m {
+            Message::Symbol | Message::Upper => State::Yell,
+            Message::Lower => State::ElseLow,
+            _ => s
+        },
+        State::ElseLow => match m {
+            Message::Question => State::QuestLow,
+            _ => s
+        },
+        State::Else => match m {
+            Message::Upper => State::Yell,
+            Message::Lower => State::ElseLow,
+            Message::Question => State::Quest,
+            _ => s
+        }
+    }
+}
+
+pub fn reply(message: &str) -> &str {
+    let state = message.chars().fold(State::Nothing, |s, c| process(s,to_message(c)));
+    match state {
+        State::Nothing => "Fine. Be that way!",
+        State::QuestLow | State::Quest => "Sure.",
+        State::Yell => "Whoa, chill out!",
+        State::YellQ => "Calm down, I know what I'm doing!",
+        _ => "Whatever."
+    }
+}