Template:Ifexpr
With this template #ifexpr can be used in a way such that it does not strip spaces and newlines from the "then" and "else" part.
Usage
[edit]{{ifexpr|2<3| p | q }}gives " p "{{ifexpr|2>3| p | q }}gives " q "{{ifexpr|2{{=}}3| p | q }}gives " q "{{ifexpr||1=2=3| p | q }}gives " q "
Compare:
{{#ifexpr:2<3| p | q }}gives "p"
Note that, unlike parser functions, templates require writing equals signs in values of unnamed parameters as {{=}}
For full substitution, simply use subst: or safesubst:. If the condition contains a parser function, template, or variable, that should be substituted too. Optionally the "then" or "else" part can also be substituted.
Error messages (examples):
{{ifexpr|1234>e3|1|0}}gives{{if|1|...}}may not be evaluated due incorrect parameter 1.{{#ifexpr:1234>e3|1|0}}gives Expression error: Unexpected number.
Expansion depth limit
[edit]13 levels allowed:
{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|a}}}}}}}}}}}}}}}}}}}}}}}}}} gives a
{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|{{ifexpr|1|a}}}}}}}}}}}}}}}}}}}}}}}}}}}} gives a
Internal technical details
[edit]For evaluating the condition the template uses the actual parser functions; however, not directly with p and q, because this strips spaces and newlines from them, but with index values 1 and 2. The result can be 1, 2, or an error message. Using a switch these are converted to p1, p2, and if/errmsg, respectively. The template with the applicable name is called (Template:P1, Template:P2, or Template:If/errmsg), with as parameters p, q, and {{{1}}}. Templates p1 and p2 ignore {{{1}}}; template if/errmsg is only called in the case of a wrong expression {{{1}}}; it ignores p and q and uses {{{1}}} for display in the error message.
Condition
[edit]#ifexpr:
[edit]Condition: non-zero.[1]
Empty gives false. Other strings which are not correct numerical or Boolean expressions give an error message[2]:
16 'pfunc_expr_stack_exhausted' => 'Expression error: Stack exhausted', 17 'pfunc_expr_unexpected_number' => 'Expression error: Unexpected number', 18 'pfunc_expr_preg_match_failure' => 'Expression error: Unexpected preg_match failure', 19 'pfunc_expr_unrecognised_word' => 'Expression error: Unrecognised word "$1"', 20 'pfunc_expr_unexpected_operator' => 'Expression error: Unexpected $1 operator', 21 'pfunc_expr_missing_operand' => 'Expression error: Missing operand for $1', 22 'pfunc_expr_unexpected_closing_bracket' => 'Expression error: Unexpected closing bracket', 23 'pfunc_expr_unrecognised_punctuation' => 'Expression error: Unrecognised punctuation character "$1"', 24 'pfunc_expr_unclosed_bracket' => 'Expression error: Unclosed bracket', 25 'pfunc_expr_division_by_zero' => 'Division by zero', 26 'pfunc_expr_invalid_argument' => 'Invalid argument for $1: < -1 or > 1', 27 'pfunc_expr_invalid_argument_ln' => 'Invalid argument for ln: <= 0', 28 'pfunc_expr_unknown_error' => 'Expression error: Unknown error ($1)', 29 'pfunc_expr_not_a_number' => 'In $1: result is not a number',