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288
       
 
       


     

       
289
       
 
       
If some values are instances of more than one of the types, it is not possible to distinguish which type they are meant to be instances of. If that's needed, consider using a [sum type](#sec-option-types-sums).

     

       
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292
       
 
       


     

       
293
       
 
       
## Sum types {#sec-option-types-sums}

     
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364
       
 
       
    This is one possible representation of what may be called a _tagged union_ or _sum type_.

     

       
365
       
 
       
    `attrTag` can be thought of as an extension of *`enum`* where the permissible items

     

       
366
       
 
       
    are attribute names, and each item is paired with a value of a specific type.

     

       
367
       
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368
       
-
       
`types.either` *`t1 t2`*

     

       
369
       
-
       


     

       
370
       
-
       
:   Type *`t1`* or type *`t2`*, e.g. `with types; either int str`.

     

       
371
       
-
       
    Multiple definitions cannot be merged.

     

       
372
       
-
       


     

       
373
       
-
       
`types.oneOf` \[ *`t1 t2`* ... \]

     

       
374
       
-
       


     

       
375
       
-
       
:   Type *`t1`* or type *`t2`* and so forth, e.g.

     

       
376
       
-
       
    `with types; oneOf [ int str bool ]`. Multiple definitions cannot be

     

       
377
       
-
       
    merged.

     

       
378
       
 
       


     

       
379
       
 
       
`types.coercedTo` *`from f to`*

     

       
380
       
 
       


     

···

       
288
       
 
       


     

       
289
       
 
       
If some values are instances of more than one of the types, it is not possible to distinguish which type they are meant to be instances of. If that's needed, consider using a [sum type](#sec-option-types-sums).

     

       
290
       
 
       


     

       
291
       
+
       
`types.either` *`t1 t2`*

     

       
292
       
+
       


     

       
293
       
+
       
:   Type *`t1`* or type *`t2`*, e.g. `with types; either int str`.

     

       
294
       
+
       
    Multiple definitions cannot be merged.

     

       
295
       
+
       


     

       
296
       
+
       
`types.oneOf` \[ *`t1 t2`* ... \]

     

       
297
       
+
       


     

       
298
       
+
       
:   Type *`t1`* or type *`t2`* and so forth, e.g.

     

       
299
       
+
       
    `with types; oneOf [ int str bool ]`. Multiple definitions cannot be

     

       
300
       
+
       
    merged.

     

       
301
       
 
       


     

       
302
       
 
       


     

       
303
       
 
       
## Sum types {#sec-option-types-sums}

     
···

       
374
       
 
       
    This is one possible representation of what may be called a _tagged union_ or _sum type_.

     

       
375
       
 
       
    `attrTag` can be thought of as an extension of *`enum`* where the permissible items

     

       
376
       
 
       
    are attribute names, and each item is paired with a value of a specific type.

     

       
0
       
 
       

     

       
0
       
 
       

     

       
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0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
377
       
 
       


     

       
378
       
 
       
`types.coercedTo` *`from f to`*

     

       
379