shithub: limbobyexample

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add isolated pick tag adt example

--- a/Generics/generics.b

+++ b/Generics/generics.b

@@ -14,12 +14,24 @@

 	init: fn(nil: ref Draw->Context, nil: list of string);

 };

+# Polymorphic type

 Rd: adt[T] {

 	t:	ref Iobuf;

 	ws:	fn(rd: self ref Rd[T]): int;

 };

-# Polymorphic type

+Num: adt {

+	pick {

+		String =>

+			s: string;

+		Int =>

+			d: int;

+	}

+

+	stringify: fn(v: self ref Num): string;

+};

+

+# Polymorphic and pick-tagged type

 Word: adt[T] {

 	w: T;

@@ -50,12 +62,18 @@

 	c := rd.ws();

 	print("Broke on '%c'\n", c);

+	d := ref Num.Int(5);

+	s := ref Num.String("Five");

+

+	print("%s\n", d.stringify());

+	print("%s\n", s.stringify());

+

 	words: list of ref Word[Int].String;

 	smiley := "☺";

 	frowny := ":(";

-	sword := ref Word[Int].String(Int(5), smiley);

+	sword := ref Word[Int].String(Int(9), smiley);

 	# Format is: Adt[Type].PickTag(fields...)

 	words = sword :: words;

@@ -78,6 +96,17 @@

 Word[T].eq(a, b: ref Word): int

 {

 	return a.w == b.w;	# This is a shallow comparison, don't rely on this

+}

+

+Num.stringify(v: self ref Num): string {

+	pick xv := v {

+	String =>

+		return xv.s;

+	Int =>

+		return string xv.d;

+	* =>

+		raise "type error";

+	}

 }

 # Matches whitespace characters