diff options
Diffstat (limited to 'runtime/doc/eval.txt')
| -rw-r--r-- | runtime/doc/eval.txt | 48 |
1 files changed, 44 insertions, 4 deletions
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt index fe15ba6115..351690f4df 100644 --- a/runtime/doc/eval.txt +++ b/runtime/doc/eval.txt @@ -93,7 +93,27 @@ non-zero number it means TRUE: > :" executed To test for a non-empty string, use empty(): > :if !empty("foo") -< + +< *falsy* *truthy* +An expression can be used as a condition, ignoring the type and only using +whether the value is "sort of true" or "sort of false". Falsy is: + the number zero + empty string, blob, list or dictionary +Other values are truthy. Examples: + 0 falsy + 1 truthy + -1 truthy + 0.0 falsy + 0.1 truthy + '' falsy + 'x' truthy + [] falsy + [0] truthy + {} falsy + #{x: 1} truthy + 0z falsy + 0z00 truthy + *non-zero-arg* Function arguments often behave slightly different from |TRUE|: If the argument is present and it evaluates to a non-zero Number, |v:true| or a @@ -841,9 +861,12 @@ All expressions within one level are parsed from left to right. ------------------------------------------------------------------------------ -expr1 *expr1* *ternary* *E109* +expr1 *expr1* *ternary* *falsy-operator* *??* *E109* + +The ternary operator: expr2 ? expr1 : expr1 +The falsy operator: expr2 ?? expr1 -expr2 ? expr1 : expr1 +Ternary operator ~ The expression before the '?' is evaluated to a number. If it evaluates to |TRUE|, the result is the value of the expression between the '?' and ':', @@ -866,6 +889,23 @@ To keep this readable, using |line-continuation| is suggested: > You should always put a space before the ':', otherwise it can be mistaken for use in a variable such as "a:1". +Falsy operator ~ + +This is also known as the "null coalescing operator", but that's too +complicated, thus we just call it the falsy operator. + +The expression before the '??' is evaluated. If it evaluates to +|truthy|, this is used as the result. Otherwise the expression after the '??' +is evaluated and used as the result. This is most useful to have a default +value for an expression that may result in zero or empty: > + echo theList ?? 'list is empty' + echo GetName() ?? 'unknown' + +These are similar, but not equal: > + expr2 ?? expr1 + expr2 ? expr2 : expr1 +In the second line "expr2" is evaluated twice. + ------------------------------------------------------------------------------ expr2 and expr3 *expr2* *expr3* @@ -2499,7 +2539,7 @@ This does NOT work: > |List| item. *:let=<<* *:let-heredoc* - *E990* *E991* *E172* *E221* + *E990* *E991* *E172* *E221* *E1145* :let {var-name} =<< [trim] {endmarker} text... text... |