srfi.69 - Basic hash tables ¶This module has been superseded by R7RS scheme.hash-table
(see scheme.hash-table - R7RS hash tables). New code should use it instead.
This is a thin adaptor on Gauche’s built-in hashtables
(see Hashtables). This is provided for the compatibility
to the portable libraries; the hashtable object created by
this module’s make-hash-table is the same as the one
created by Gauche’s built-in, and you can pass the table to
both APIs.
Here’s a summary of difference between SRFI-69 and Gauche’s built-in hash table API:
make-hash-table, as well as alist->hash-table,
takes equality predicate and hash function, instead of a single
comparator argument as Gauche does.
make-hash-table
takes two arguments, an object to calculate a hash value,
and a positive integer that limits the range of the hash value.
hash-table-ref,
which takes a thunk to be called when the table doesn’t have an
entry for the given key, while Gauche’s hash-table-get takes
a fallback value for that.
SRFI-69 also has hash-table-ref/default,
which takes a fallback value like Gauche’s hash-table-get,
but the default value can’t be omitted.
hash-table-update! and hash-table-update!/default
to Gauche’s hash-table-update! is the same as
hash-table-ref, hash-table-ref/default and
hash-table-get.
hash-table-walk,
which is Gauche’s hash-table-for-each. The srfi name is chosen
to avoid conflict with existing Scheme implementations.
The following procedures are the same as Gauche’s built-in ones. See Hashtables, for the details.
hash-table? hash-table-delete! hash-table-exists? hash-table-keys hash-table-values hash-table-fold hash-table->alist hash-table-copy
[SRFI-69]{srfi.69}
Creates a new hashtable and returns it. This is the same name
as Gauche’s built-in procedure, but the arguments are different.
The eq-pred argument is an equality predicate; it takes
two arguments and returns #t if two are the same,
and #f if not. When omitted, equal? is used.
The hash-proc argument is a hash function.
It takes two arguments: an object to hash, and a positive
integer to limit the range of the hash value. (Note that
Gauche’s native hash functions takes only one argument.)
When omitted, Gauche tries to choose appropriate hash function
if eq-pred is known one (eq?, eqv?,
equal?, string=? or string-ci=?).
Otherwise we use scheme.hash-table’s hash procedure
(see scheme.hash-table - R7RS hash tables).
But there’s no guarantee that the generic hash
works appropriately; you should give
suitable hash-proc if you pass custom eq-pred.
The returned hash table is an instance of Gauche’s native hash table. You can pass it to Gauche’s builtin procedures.
SRFI-69 allows implementation-specific arguments args to be
passed to make-hash-table. At this moment, Gauche
ignores them.
[SRFI-69]{srfi.69}
Like Gauche’s builtin alist->hash-table, but takes
eq-pred and hash-fn separately,
instead of a single comparator.
The alist argument is a list of pairs. The car of each pair is used for a key, and the cdr for its value.
See make-hash-table above for the description of
eq-pred, hash-fn and args.
[SRFI-69]{srfi.69}
Returns equivalence function and hash function of the
hashtable ht.
Note that SRFI-69’s hash function takes an optional bound argument. Since our underlying hash tables don’t use bound argument, we actually wrap the internal hash function to allow the optional bound argument.
[SRFI-69]{srfi.69}
Looks up the value corresponding to key in a hash table ht.
If there’s no entry for key, thunk is called
without arguments, and its result is returned.
The default of thunk is to signal an error.
This convention differs from Gauche’s built-in hash-table-get,
which takes optonal default argument to be returned when the key
doesn’t exist (see Hashtables). The following equivalence holds:
(hash-table-get ht key default) ≡ (hash-table-ref ht key (^[] default))
[SRFI-69]{srfi.69}
Looks up the value corresponding to key in a hash table ht.
If the key doesn’t exist, default is returned.
This is like Gauche’s hash-table-get, but default can’t be
omitted (see Hashtables).
[SRFI-69]{srfi.69}
This is the same as Gauche’s hash-table-put! (see Hashtables).
[SRFI-69]{srfi.69}
Calls proc with the value associated to key in ht,
and replace the value in ht with the result of proc.
The following functional equivalences hold, though these procedures
may be more efficient.
(hash-table-update! ht key proc thunk) ≡ (hash-table-set! ht key (proc (hash-table-ref ht key thunk))) (hash-table-update!/default ht key proc default) ≡ (hash-table-set! ht key (proc (hash-table-ref/default ht key default)))
Note that Gauche’s built-in hash-table-update! is different, for
it takes optional default argument instead of thunk
(see Hashtables).
[SRFI-69]{srfi.69}
Returns the number of entries in a hash table ht. The same as Gauche’s
hash-table-num-entries.
[SRFI-69]{srfi.69}
For each entry in a hash table ht,
calls proc with two arguments, a key and its value.
It’s the same as Gauche’s hash-table-for-each.
[SRFI-69]{srfi.69}
Add all entries in a hash table ht2 into a hash table ht1,
and returns ht1. Note that ht1 is destructively modified.
If an entry with the same key exists in both ht1 and ht2,
its value in ht1 is replaced with ht2’s.
[SRFI-69]{srfi.69}
Like Gauche’s hash, except this one can take bound argument;
if provided, it must be a positive integer, and the return value
is limited between 0 and (- bound 1), inclusive.
[SRFI-69]{srfi.69}
These are like SRFI-13’s (see srfi.13 - String library), except
these don’t take start and end argument.
[SRFI-69]{srfi.69}
This is Gauche’s eq-hash, except this one can take bound argument.