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Add Nothing' to Maybe.gf, including warning

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john.j.camilleri
2014-07-02 06:37:27 +00:00
parent b9ffc8ac00
commit f189e91629
1 changed files with 13 additions and 7 deletions
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20
lib/src/prelude/Maybe.gf
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@@ -9,21 +9,27 @@ resource Maybe = open Prelude, Predef in {
-- Constructors
Maybe : (t : Type) -> Type = \t -> {
inner : t ;
exists : Bool
exists : Bool ;
} ;
Just : (T : Type) -> T -> Maybe T = \_,t -> {
inner = t ;
exists = True
exists = True ;
} ;
-- Nothing : (T : Type) -> Maybe T = \_ -> {
-- inner = variants {} ;
-- exists = False
-- } ;
Nothing : (T : Type) -> T -> Maybe T = \_,t -> {
inner = t ;
exists = False
exists = False ;
} ;
-- IMPORTANT
-- This version of Nothing would be preferred, but it may not work as expected.
-- This happens when using Nothing within a record. For discussion of this see:
-- https://groups.google.com/d/msg/gf-dev/KAQEttN-0Cs/EjGHjOXEKO0J
Nothing' : (T : Type) -> Maybe T = \_ -> {
inner = variants {} ;
exists = False ;
} ;
-- You have been warned!
-- Functions
exists : (T : Type) -> Maybe T -> Bool = \_,m -> m.exists ;
isJust : (T : Type) -> Maybe T -> Bool = \_,m -> m.exists ;