6.2 Strings

6.2.1 String Creation and Copying

The following are built-in string creation and copying functions:

(allocate-string SIZE:integer): string expr
Constructs and returns a string with SIZE characters. The contents of the string are not initialized.

(make-string SIZE:integer INITVAL:integer): string expr
Constructs and returns a string with SIZE characters, each initialized to the ASCII code INITVAL.

(mkstring UPLIM:integer INITVAL:integer): string expr
An old form of make-string. Returns a string of characters all initialized to INITVAL, with upper bound UPLIM. The returned string contains a total of (add1 UPLIM) characters.

(string [ARGS:integer]): string nexpr
Create string of elements from a list of ARGS.
    1 lisp> (string 65 66 67)  

(copystringtofrom NEW:string OLD:string): NEW:string expr
Copy all characters from old into new. This function is destructive.

(copystring S:string): string expr
Copy to new string, allocating space.

6.2.2 About the Basic String Operations

The representation of strings is very similar to that of vectors. Due to this similarity, there are functions which may be applied to either data type. Such functions provide primitive operations on strings. PSL provides many other functions specific to strings which are defined in various library modules.

6.2.3 The Operations

This section documents functions in the library module slow-strings (s-strings). There is another library module called fast-strings (f-strings). The fast-strings module provides alternate definitions for these functions. When the switch fast-strings is non-nil the compiler will use these alternate definitions to produce efficient code. However, there will not be any verification that arguments are of correct type (in addition, it is assumed that numeric arguments are within a proper range). If invalid arguments are used, then at best your code will not generate correct results, you may actually damage the PSL system. There are two side effects to loading fast-strings The slow-strings module will be loaded and the switch fast-strings will be set to t. For more information on the switch fast-strings see Chapter 19.

(string-fetch S:string I:integer): any expr
Accesses an element of a PSL string. Indexes are zero based. The ASCII character stored in that position of the string is returned.

Characters are represented by inums. You should not rely on this when you write code. Such code cannot be easily transported to other systems where either the encoding is different or where characters are a seperate data type.

(string-store S:string I:integer X:char): None Returned expr
Stores into a PSL string. String indexes start with 0.

(string-length S:string): integer expr
Returns the number of elements in a PSL string. Since indexes start with index 0, the size is one larger than the greatest legal index. Compare this function with string-upper-bound, documented below.

(string-upper-bound S:string): integer expr
Returns the greatest legal index for accessing or storing into a PSL string. Compare this function with string-length, documented above.

(string-empty? S:string): boolean expr
True if the string has no elements (its size is 0), otherwise nil.