People,
I thank Ralf Hemmecke for explanations.
I look into the book, and use the Axiom brouser. And still it is
difficult to find some simple constructs.
I have the following beginner questions.
1. Where can be found simple examples of Spad programs?
For example, in Haskell, the Standard Library description is full
of such examples. They are the meaning definitions,
and also Haskell program examples,
and most often, they are also efficient implementation.
2. What Spad has for the Direct Product of (different) types?
For example, in Haskell, I write
span :: (a -> Bool) -> [a] -> ([a], [a]),
zipRem :: [a] -> [a] -> ([a], [a], [a]).
Here `a' denotes any type (a parameter),
(a -> Bool) is the type of functions from a to Bool,
[a] === List a is the type of lists over a,
([a], [a]) === Pair [a] [a]
is the direct product of the two list types,
(a, b, c) is the direct product of the three free types,
For example,
("bc", 2, 'd') is a triple which is an element of the type
(String, Integer, Char),
the second member can be extracted by an anonymous function as
(\ (_, y, _) -> y),
and it can be set as (\ y' (x, y, z) -> (x, y', z)).
Which are the corresponding type constructors and data operations in
Spad ?
Thus, I tried for `span' the code
)abbrev package MY-LIST MyList
MyList(T : Type) : with
span : (T -> Boolean) -> List T -> DirectProduct(2, List T)
==
add
span p xs ==
empty? xs => ([], xs)
...
But, probably, DirectProduct and `([], xs)' is not the point ...
3. List Character vs String
Haskell puts type String = [Char]
-- a string is a list of characters.
For example,
"ab;c\nd" === ['a', 'b', ';', 'c', '\n', 'd'].
Due to this, most of the functions for String are done by generic
functions for the types
forall a => [a], (Eq a) => [a], (Ord a) => [a].
I hope to program strings in Spad by using the conversion
String <--> List Character.
For `-->', I find `entries' in "String", "operations".
Does it fit?
And what is for `<--' ?
Thank you in advance for explanation,
------
Sergei
[email protected]
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