Generic way to safeguard an expression
- Note: I'm leaving this standing for completeness' sake, but recent versions of ParserFunction include
{{#iferror:expression|error|success}}, or, shorter, {{#iferror:expression}} - the latter of which returns the expression only if it is valid. Once LGPedia's ParserFunctions are updated, this subsection is obsolete.
This code can be used to protect parameters in mathematical templates, to make sure the input is either numerical or a valid expression.
{{#ifeq: {{#ifexpr: {{{1}}} |true|true}} | true | Is expression | Is not an expression}}
This code works by having ifeq determine whether the output of ifexpr is the string "true", and determining the output based on the outcome. ifexpr always returns "true" if {{{1}}} is a valid expression, no matter if said expression itself is true or false. If the expression is not valid, ifexpr generates an error string, which unequals "true" and thus triggers ifeq's false part.
Logical AND, OR, XOR
For the moment, the only way to create logical ANDs, ORs or XORs seems to be nested ifs and ifeqs inside an ifexpr. In this technique, we are outputting 1s and 0s depending on the state of our parameters, and thereby create a normal expression solvable by ifexpr. All examples can be combined, subgroups can be created through parenthesis, and parameter names and control values can be replaced, as long as it happens consistently throughout the entire expression.
Pieces
{{ #ifeq: {{{1}}} | CONTROL VALUE | 1 | 0 }}{{ #if: {{{1|}}} | 1 | 0 }}{{ #ifexpr: EXPRESSION | TRUE | FALSE }}
Test on state
- Logical AND:
{{ #ifexpr: {{ #if: {{{1|}}} | 1 | 0 }} and {{ #if: {{{2|}}} | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if both {{{1}}} and {{{2}}} are defined.
- Logical OR:
{{ #ifexpr: {{ #if: {{{1|}}} | 1 | 0 }} or {{ #if: {{{2|}}} | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if either {{{1}}} or {{{2}}} or both are defined.
- Logical XOR:
{{ #ifexpr: {{ #if: {{{1|}}} | 1 | 0 }} != {{ #if: {{{2|}}} | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if either {{{1}}} or {{{2}}} but not both are defined.
Test on control value
In this example, the control value is "yes".
- Logical AND:
{{ #ifexpr: {{ #ifeq: {{{1}}} | yes | 1 | 0 }} and {{ #ifeq: {{{2}}} | yes | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if both {{{1}}} and {{{2}}} are set to "yes".
- Logical OR:
{{ #ifexpr: {{ #ifeq: {{{1}}} | yes | 1 | 0 }} or {{ #ifeq: {{{2}}} | yes | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if either {{{1}}} or {{{2}}} or both are set to "yes".
- Logical XOR:
{{ #ifexpr: {{ #ifeq: {{{1}}} | yes | 1 | 0 }} != {{ #ifeq: {{{2}}} | yes | 1 | 0 }} | TRUE | FALSE }}
- Returns TRUE if either {{{1}}} or {{{2}}} but not both are set to "yes".
