enums and match (in the compiler written in Finch)

enum Color { Red, Green, Blue }   enum Status { Ok = 200, NotFound = 404 }

Color.Red, Color(n) (checked), int(c), == and != only, printed by name, usable as
map keys and struct fields, with methods (fn Color.next()).

match value { Red, Green -> ... Blue -> ... else -> ... } as a statement, or as an
expression that gives a value. Works on enums, whole numbers, chars, text and bools;
a match on an enum has to handle every variant or end with else, and says which are
missing. A bare variant name (Red) is enough inside a match on an enum.

Only the self-hosted compiler has them; tests/new holds their tests, tests/run stays what
the C++ compiler also runs. boot.sh: 31 passed.

tests/new/enums.fch

@@ -0,0 +1,75 @@
+enum Color { Red, Green, Blue }
+enum Status { Ok = 200, NotFound = 404, Teapot = 418 }
+
+struct Pixel {
+    Color color
+    int x
+}
+
+fn Color.warm() -> bool {
+    return self == Color.Red
+}
+
+fn Color.next() -> Color {
+    if self == Color.Red {
+        return Color.Green
+    }
+    if self == Color.Green {
+        return Color.Blue
+    }
+    return Color.Red
+}
+
+fn describe(Color c) -> str {
+    return match c {
+        Red -> "red"
+        Green -> "green"
+        Blue -> "blue"
+    }
+}
+
+fn code(Status s) -> str {
+    match s {
+        Status.Ok -> return "fine"
+        Status.NotFound, Status.Teapot -> return "odd"
+    }
+}
+
+fn main() {
+    c := Color.Green
+    print(c, Color.Blue, int(Color.Blue), int(Status.Teapot))
+    print(c == Color.Green, c != Color.Green)
+    print(describe(Color.Red), describe(c.next()), c.warm(), Color.Red.warm())
+    print(code(Status.Ok), code(Status.NotFound))
+    p := Pixel(color: Color.Blue, x: 3)
+    print(p)
+    []Color all = [Color.Red, Color.Blue]
+    print(all, all.len)
+    for col in all {
+        match col {
+            Color.Red -> print("a red one")
+            else -> print("something else")
+        }
+    }
+    s := Status(404)
+    print(s, Status(200))
+    n := 5
+    kind := match n {
+        1, 2, 3 -> "small"
+        4, 5 -> "medium"
+        else -> "large"
+    }
+    print(kind)
+    word := "two"
+    match word {
+        "one" -> print(1)
+        "two" -> {
+            print(2)
+            print("two!")
+        }
+        else -> print("many")
+    }
+    counts := [Color.Red: 2, Color.Blue: 5]
+    print(counts[Color.Blue], counts)
+    print(str(Color.Green) + "!")
+}

tests/new/enums.out

@@ -0,0 +1,14 @@
+Green Blue 2 418
+true false
+red blue false true
+fine odd
+Pixel(color: Blue, x: 3)
+[Red, Blue] 2
+a red one
+something else
+NotFound Ok
+medium
+2
+two!
+5 {Red: 2, Blue: 5}
+Green!

tests/new/fail/enum_bad_number.fch

@@ -0,0 +1,6 @@
+// expect: 7 is not the number of any variant of Color
+enum Color { Red, Green }
+
+fn main() {
+    print(Color(7))
+}

tests/new/fail/enum_compare_order.fch

@@ -0,0 +1,6 @@
+// expect: enums can only be compared with == and !=
+enum Color { Red, Green }
+
+fn main() {
+    print(Color.Red < Color.Green)
+}

tests/new/fail/enum_no_variant.fch

@@ -0,0 +1,6 @@
+// expect: the enum Color has no variant 'Blue'
+enum Color { Red, Green }
+
+fn main() {
+    print(Color.Blue)
+}

tests/new/fail/match_arm_after_else.fch

@@ -0,0 +1,8 @@
+// expect: this arm can never be used
+fn main() {
+    n := 3
+    match n {
+        else -> print("any")
+        1 -> print("one")
+    }
+}

tests/new/fail/match_arms_differ.fch

@@ -0,0 +1,9 @@
+// expect: the arms of a match have to give the same type
+fn main() {
+    n := 3
+    x := match n {
+        1 -> "one"
+        else -> 2
+    }
+    print(x)
+}

tests/new/fail/match_missing_variant.fch

@@ -0,0 +1,10 @@
+// expect: doesn't handle Blue
+enum Color { Red, Green, Blue }
+
+fn main() {
+    c := Color.Red
+    match c {
+        Red -> print(1)
+        Green -> print(2)
+    }
+}

tests/new/fail/match_needs_else.fch

@@ -0,0 +1,8 @@
+// expect: needs an 'else' arm
+fn main() {
+    n := 3
+    match n {
+        1 -> print("one")
+        2 -> print("two")
+    }
+}

tests/new/fail/match_not_a_variant.fch

@@ -0,0 +1,11 @@
+// expect: 'Purple' is not a variant of Color
+enum Color { Red, Green }
+
+fn main() {
+    c := Color.Red
+    match c {
+        Red -> print(1)
+        Purple -> print(2)
+        else -> print(3)
+    }
+}