exists

exists( 
s_formalVar 
l_valueList 
g_predicateExpr 
)
=> g_result
exists( 
s_key 
o_table 
g_predicateExpr 
)
=> t / nil

Description

Returns the first tail of l_valueList whose car satisfies a predicate expression. Also verifies whether an entry in an association table satisfies a predicate expression. This is a syntax form.

This process continues to apply the cdr function successively through l_valueList until it finds a list element that causes g_predicateExpr to evaluate to non-nil. It then returns the tail that contains that list element as its first element.

This function can also be used to verify whether an entry in an association table satisfies g_predicateExpr.

Arguments

s_formalVar	Local variable that is usually referenced in g_predicateExpr.
l_valueList	List of elements that are bound to s_formalVar, one at a time.
g_predicateExpr	SKILL expression that usually uses the value of s_formalVar.
s_key	Key portion of an association table entry.
o_table	Association table containing the entries to be processed.

Value Returned

g_result	First tail of l_valueList whose car satisfies g_predicateExpr.
nil	If none of the elements in l_valueList can satisfy it.
t	Entry in an association table satisfies g_predicateExpr.

Examples

Tests an association table and verifies the existence of an entry where both the key and its corresponding value are of type string.

exists( x '(1 2 3 4) (x > 1) )  
=> (2 3 4)

exists( x '(1 2 3 4) (x > 4) ) 
=> nil

exists( key myTable (and (stringp key)
             (stringp myTable[key])))
=> t

Related Topics

Flow Control Functions

car

cdr

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