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Add from-optional function #1327

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Add from-optional function #1327

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8 changes: 8 additions & 0 deletions library/optional.lisp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
(#:cell #:coalton-library/cell)
(#:iter #:coalton-library/iterator))
(:export
#:from-optional
#:from-some
#:some?
#:none?))
Expand All @@ -23,6 +24,13 @@
;; Optional
;;

(declare from-optional (:a -> (Optional :a) -> :a))
(define (from-optional def opt)
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Personally I think maybe the variable should be 'default' for clarity

"Get the value of OPT, or return DEF if OPT is None."
(match opt
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This function has some overlap with 'unwrap-or-else', though I think that this may be a better syntax if you're not applying anything to the unwrapped element.

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It may be worth abstracting this so it could work for Result too, maybe make a function 'unwrap-or-default' that work for anything satisfying the 'unwrappable' class.

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Actually that abstraction already exists:

coalton/library/classes.lisp

Line 321 in 19965eb

(define (with-default default container)

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Ah! Drat - I was afraid this was already covered by something I couldn't find. This PR probably adds no value then.

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Yeah, I'm going to go ahead and close. Thanks!

((Some x) x)
((None) def)))

(declare from-some (String -> (Optional :a) -> :a))
(define (from-some str opt)
"Get the value of OPT, erroring with the provided string if it is None."
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2 changes: 2 additions & 0 deletions library/prelude.lisp
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Expand Up @@ -130,10 +130,12 @@

(:import-from
#:coalton-library/optional
#:from-optional
#:from-some
#:some?
#:none?)
(:export
#:from-optional
#:from-some
#:some?
#:none?)
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