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docs: Basic information about match-ref

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Erik Svedäng 2020-12-23 09:55:31 +01:00
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docs/LanguageGuide.md
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@ -177,7 +177,8 @@ and other static analysis. The first three of them are also available in dynamic
(while <expression> <body>) ;; Loop until expression is false
(use <module>) ;; Brings all symbols inside <module> into the scope
(with <module> <expr1> <expr2> ...) ;; Locally scoped `use` statement where all expressions after it will look up symbols in the <module>
(match <expression> <case1> <expr1> <case2> <expr2> ...) ;; Pattern matches <expression> against a set of sumtype constructors
(match <expression> <case1> <expr1> <case2> <expr2> ...) ;; Pattern matches an <expression> against a set of sumtype constructors
(match-ref <expression> <case1> <expr1> <case2> <expr2> ...) ;; Pattern matches an <expression> of reference type, not taking ownership of its members
(ref <expression>) ;; Borrow an owned value
(address <expression>) ;; Takes the memory address of a value, returns a C-style pointer
(set! <variable> <expression>) ;; Mutate a variable
@ -368,6 +369,17 @@ You can use pattern matching to extract values in a safe way:
_ (logic-other)))
```
Note that match works with *values* (not references) takes ownership over the value being matched on. If you instead want to match on a reference, you can use `match-ref`:
```clojure
(match-ref &might-be-a-string
(Just s) (IO.println s)
Nothing (IO.println "Got nothing"))
```
Note that this code would not take ownership over `might-be-a-string`. Also, the `s` in the first case is a reference, since it wouldn't be safe to destructure the `Maybe` into values in this situation.
### C Interop
```clojure
(system-include "math.h") ;; compiles to #include <math.h>