5. Bigloo -- Standard Library<br>5.6 Hash Tables

5. Bigloo -- Standard Library 5.6 Hash Tables

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Home: | Bigloo A ``practical Scheme compiler'' User manual for version 2.6b December 2003
Previous chapter: | Core Language
Next chapter: | Pattern Matching
Standard Library
5.1 | Scheme Library
| 5.1.1 | Booleans
| 5.1.2 | Equivalence predicates
| 5.1.3 | Pairs and lists
| 5.1.4 | Symbols
| 5.1.5 | Keywords
| 5.1.6 | Numbers
| 5.1.7 | Characters
| 5.1.8 | UCS-2 Characters
| 5.1.9 | Strings
| 5.1.10 | Unicode (UCS-2) Strings
| 5.1.11 | Vectors
| 5.1.12 | Control features
5.2 | Input and output
5.3 | Structures and Records
| 5.3.1 | Structures
| 5.3.2 | Records (SRFI-9)
5.4 | Serialization
5.5 | Bit manipulation
5.6 | Hash Tables
| 5.6.1 | Hash tables
| 5.6.2 | Deprecated Hash tables
5.7 | System programming
| 5.7.1 | Operating System interface
| 5.7.2 | Files
5.8 | Process support
5.9 | Socket support
5.10 | Date
5.11 | Posix Regular Expressions
| 5.11.1 | Regular Expressions Procedures
| 5.11.2 | Regular Expressions Pattern Language
| 5.11.3 | An Extended Example
Chapters
| Acknowledgements
1. | Table of contents
2. | Overview of Bigloo
3. | Modules
4. | Core Language
5. | Standard Library
6. | Pattern Matching
7. | Object System
8. | Threads
9. | Regular parsing
10. | Lalr(1) parsing
11. | Errors and Assertions
12. | Eval and code interpretation
13. | Macro expansion
14. | Command Line Parsing
15. | Explicit typing
16. | The C interface
17. | The Java interface
18. | Bigloo Libraries
19. | Extending the Runtime System
20. | SRFIs
21. | DSSSL support
22. | Compiler description
23. | User Extensions
24. | Bigloo Development Environment
25. | Global Index
26. | Library Index
| Bibliography
| ### 5.6.1 Hash tables Bigloo offers hash tables. Here are described functions which define and use them.
make-hashtable [bucket-len] [max-bucket-len] | bigloo procedure
Defines an hash table for which the number of buckets is `bucket-len`. The variable `max-bucket-len` specify when the table should be resized. If provided, these two values have to be exact integers greater or equal to 1. Normally you could ignore `bucket-len` and `max-bucket-len` arguments and call `make-hashtable` with no argument at all.

hashtable? obj | bigloo procedure
Returns `#t` if `obj` is an hash table, constructed by `make-hashtable`.

hashtable-size table | bigloo procedure
Returns the number of entries contained in `table`.

hashtable-get table key | bigloo procedure
Returns the entry whose key is `key` in `table`. If not entry is found `#f` is returned.

hashtable-put! table key obj | bigloo procedure
Puts `obj` in `table` under the key `key`. This function returns the object bound in the table. If there was an object `obj-old` already in the table with the same key as `obj`, this function returns `obj-old`; otherwise it returns `obj`.

hashtable-remove! table key | bigloo procedure
Removes the object associated to `key` from `table`, returning `#t` if such object was bound in table and `#f` otherwise.

hashtable-update! table key update-fun init-value | bigloo procedure
If key is already in table, the new value is calculated by `(update-fun current-value)`. Otherwise the `table` is extended by an entry linking key and `init-value`.

hashtable->vector table | bigloo procedure
hashtable->list table | bigloo procedure
Convert a hash table `table` to a vector or to a list.

hashtable-for-each table fun | bigloo procedure
Applies `fun` to each of the keys and elements of `table` (no order is specified). In consequence, `fun` must be a procedure of two arguments. The first one is a key and the second one, an associated object.

Here is an example of hash table.

    (define *table* (make-hashtable))

    (hashtable-put! *table* "toto" "tutu")
    (hashtable-put! *table* "tata" "titi")
    (hashtable-put! *table* "titi" 5)
    (hashtable-put! *table* "tutu" 'tutu)
    (hashtable-put! *table* 'foo 'foo)

    (print (hashtable-get *table* "toto"))
       -| "tutu"
    (print (hashtable-get *table* 'foo))
       -| 'foo
    (print (hashtable-get *table* 'bar))
       -| #f

    (hashtable-for-each *table* (lambda (key obj) (print (cons key obj))))
       -| ("toto" . "tutu")
          ("tata" . "titi")
          ("titi" . 5)
          ("tutu" . TUTU)
          (foo . foo)

object-hashnumber object | bigloo generic
This generic function computes a hash number of the instance `object`. Example:
    (define-method (object-hashnumber pt::point)
       (with-access::point pt (x y)
          (+fx (*fx x 10) y)))

### 5.6.2 Deprecated Hash tables

Bigloo offers hash tables. Here are described functions which define and use them.

make-hash-table ms nb gk eq [is] | bigloo procedure
Defines an hash table of maximum length `ms`. If `is` is provided, it sets the initial table size. The formal `nb` is a function which, if applied to a `key`, has to return an integer bound in interval [`0`..`ms`]. The formal `gk` is a function which, if applied to an object, returns its key. For example, the identity is a good candidate for integers, strings, symbols, etc. The last formal `eq` is a equivalence predicate which is used when searching for an entry in the table.

hash-table? obj | bigloo procedure
Returns `#t` if `obj` is an hash table.

hash-table-nb-entry table | bigloo procedure
Returns the number of entries contained in `table`.

get-hash key table | bigloo procedure
Returns the entry whose key is `key` in `table`. If not entry is found `#f` is returned.

put-hash! obj table | bigloo procedure
Puts `obj` in `table`. This function returns the object bound in the table. If there was an object `obj-old` already in the table with the same key as `obj`, this function returns `obj-old`; o therwise it returns `obj`.

rem-obj-hash! obj table | bigloo procedure
Removes `obj` from `table`, returning `#t` if such object was bound in table and `#f` otherwise.

rem-key-hash! key table | bigloo procedure
Removes an object associated with `key` in `table`, returning `#t` if such an object was bound in table and `#f` otherwise.

for-each-hash fun table | bigloo procedure
Applies `fun` to each of the elements of `table` (no order is specified).

Some functions compute hash numbers from Scheme objects:

string->0..255 string | bigloo procedure
string->0..2^x-1 string power | bigloo procedure
The formal `power` has to be a power of 2 between 1 and 16.

int->0..255 int | bigloo procedure
int->0..2^x-1 int power | bigloo procedure
obj->0..255 obj | bigloo procedure
obj->0..2^x-1 obj power | bigloo procedure

Here is an example of hash table that contains pairs:

    (define *table*
       (make-hash-table 1024
                        (lambda (o) (string->0..2^x-1 o 10))
                        (lambda (x) (car x))
                        string=?
                        64))

    (let ((cell1 (cons "toto" "tutu"))
          (cell2 (cons "tata" "titi"))
          (cell3 (cons "titi" 5))
          (cell4 (cons "tutu" 'tutu)))
       (put-hash! cell1 *table*)
       (put-hash! cell2 *table*)
       (put-hash! cell3 *table*)
       (put-hash! cell4 *table*))

    (print (cdr (get-hash "toto" *table*)))
       -| "tutu"

    (for-each-hash print *table*)
       -| ("toto" . "tutu")
          ("tata" . "titi")
          ("titi" . 5)
          ("tutu" . TUTU)

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Last update Tue Dec 16 13:46:41 2003