|
This is not hard to read.
The main novelty is pattern matching itself, which is making its way into languages that are used (java, javascript, etc) from languages that are interesting (Haskell, lisp, etc) Take a look at this example from the text, which contains an obvious domain modeling error while demonstrating cool things: def suit := algebraicDataMatcher
| spade
| heart
| club
| diamond
def card := algebraicDataMatcher
| card suit (mod 13)
def poker cs :=
match cs as multiset card with
| [card $s $n, card #s #(n-1), card #s #(n-2), card #s #(n-3), card #s #(n-4)]
-> "Straight flush"
This matches a new kind of poker hand called the "wrap around straight flush," where a straight can wrap around Q, K, A, 2, 3. assertEqual "poker hand 1"
(poker [Card Spade 3, Card Spade 2, Card Spade 1, Card Spade 0, Card Spade 12])
"Straight flush"
TRUE
IOW, in their eagerness to demonstrate a really cool match on a mod 13 expression (something I haven't seen before), the author models the domain incorrectly.It's also somewhat confusing that the cards are modeled as n-1 - ace=0, 2=1, 3=2, etc, which is also confusing. I tried for about 10 minutes to fix it, but the only notation documentation I found is math that is way over my head. |