Dot-Dot Expressions

They require StdEnum module from the Standard Environment and provide an alternative way to implicitly construct lists. They cannot be used as a pattern.

All type of lists can be constructed using Dot-Dot expressions, but the element type must be an instance of Enum class.

The full syntax has three components, but only the first component is mandatory.

// Language: Clean

[ init, next .. last ]

Usage Examples

If only init component is given, it evaluates to an infinite list. Consecutive elements differ by one unit.

// Language: Clean

x :: [ Int ]
x =  [ 1 .. ]  // [ 1, 2, 3 and so on ]

If init and last components are given, it evaluates to a finite list. Consecutive elements differ by one unit.

// Language: Clean

x :: [ Int ]
x =  [ 1 .. 4 ]  // [ 1, 2, 3, 4 ] 

If init and next components are given, it evaluates to an infinite list. Consecutive elements differ by next minus init unit.

// Language: Clean

x :: [ Int ]
x =  [ 1, 3 .. ]  // [ 1, 3, 5 and so on ]

It is possible to construct an infinite list whose elements are in descending order.

// Language: Clean

x :: [ Int ]
x =  [ 1, 0 .. ]  // [ 1, 0, -1 and so on ]

If init, next, and last components are given, it evaluates to a finite list. Consecutive elements differ by next minus init unit.

// Language: Clean

x :: [ Int ]
x =  [ 1, 3 ..7 ]  // [ 1, 3, 5, 7 ]

If the difference is positive, elements strictly greater than last are not included.

// Language: Clean

x :: [ Int ]
x =  [ 1, 3 .. 6 ]  // [ 1, 3, 5 ]

When last is greater than init but lesser than next, only init is included.

// Language: Clean

x :: [ Int ]
x =  [ 1, 3 .. 2 ]  // [ 1 ]

When last is lesser than both init and next, no element is included.

// Language: Clean

x :: [ Int ]
x =  [ 1, 3 .. 0 ]  // [ ]

If the difference is negative, elements strictly less than last are not included.

// Language: Clean

x :: [ Int ]
x =  [ 4, 2 .. -3 ]  // [ 4, 2, 0, -2 ]

When last is greater than next but lesser than init, only init is included.

// Language: Clean

x :: [ Int ]
x =  [ 3, 1 .. 2 ]  // [ 3 ]

When last is greater than both next and init, no element is included.

// Language: Clean

x :: [ Int ]
x =  [ 3, 1 .. 4 ]  // [ ]