Revisions to Is it possible to separately call the default value of a variable which isn't at the end of the sequence?

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edited Apr 13, 2017 at 12:55

1

If you only want the default values for the leading parameters (or some other order you choose), and not an arbitrary parameter at the time of the function call, you can prioritize the patterns as described here described here.

If your function does have Hold attributes you will need a slightly more complicated replacement. I will make use of RuleCondition⁽¹⁾⁽¹⁾:

Michael E2 Michael E2 showed what is perhaps the most declarative method. I don't think by itself it is as easily extensible, but then again there must be a limit to how many arguments a user is going to count anyway. Nevertheless one could automate that method with meta-programming, so let's do it.

If you only want the default values for the leading parameters (or some other order you choose), and not an arbitrary parameter at the time of the function call, you can prioritize the patterns as described here.

If your function does have Hold attributes you will need a slightly more complicated replacement. I will make use of RuleCondition⁽¹⁾:

Michael E2 showed what is perhaps the most declarative method. I don't think by itself it is as easily extensible, but then again there must be a limit to how many arguments a user is going to count anyway. Nevertheless one could automate that method with meta-programming, so let's do it.

If you only want the default values for the leading parameters (or some other order you choose), and not an arbitrary parameter at the time of the function call, you can prioritize the patterns as described here.

If your function does have Hold attributes you will need a slightly more complicated replacement. I will make use of RuleCondition⁽¹⁾:

Michael E2 showed what is perhaps the most declarative method. I don't think by itself it is as easily extensible, but then again there must be a limit to how many arguments a user is going to count anyway. Nevertheless one could automate that method with meta-programming, so let's do it.

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edited Jul 28, 2013 at 14:43

Mr.Wizard

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makeDefaults[fname_Symbol, defaults_List] := With[{par =fname Table[Unique["$"],@@@ {Length @ defaults}]}Pattern[#,  With[{set = Hold[# := #2]_] &[fname& @@/@ (Pattern[##, _]#} & /@ par)Table[Unique["$"], fname{Length @@@ par]defaults},] // Do[ ReplacePart[set, {0SetDelayed ->@@ IdentityReplacePart[#, {1, {1, n} -> Null, {1, 2, n} -> defaults[[n]]}],   {n, Length @ defaults}   ]  ]   ]&

makeDefaults[fname_Symbol, defaults_List] := With[{par = Table[Unique["$"], {Length @ defaults}]},  With[{set = Hold[# := #2] &[fname @@ (Pattern[#, _] & /@ par), fname @@ par]}, Do[ ReplacePart[set, {0 -> Identity, {1, 1, n} -> Null, {1, 2, n} -> defaults[[n]]}], {n, Length @ defaults}   ]  ]   ]

makeDefaults[fname_Symbol, defaults_List] := fname @@@ {Pattern[#, _] & /@ #, #} & @ Table[Unique["$"], {Length @ defaults}] // Do[ SetDelayed @@ ReplacePart[#, {{1, n} -> Null, {2, n} -> defaults[[n]]}],   {n, Length @ defaults} ] &

deleted 58 characters in body

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edited Jul 28, 2013 at 9:39

Mr.Wizard

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makeDefaults[fname_Symbol, defaults_List] := With[{par = Table[Unique["$"], {Length @ defaults}]}, With[{set = Hold[# := #2] &[fname @@ (Pattern[#, _] & /@ par), fname @@ par]}, Do[ ReplacePart[ setReplacePart[set,  {0 -> Identity, {1, 1, n} -> Null, {1, 2, n} -> RuleCondition @ defaults[[n]]} ], {n, Length @ defaults} ] ] ]

makeDefaults[fname_Symbol, defaults_List] := With[{par = Table[Unique["$"], {Length @ defaults}]}, With[{set = Hold[# := #2] &[fname @@ (Pattern[#, _] & /@ par), fname @@ par]}, Do[ ReplacePart[ set,  {0 -> Identity, {1, 1, n} -> Null, {1, 2, n} -> RuleCondition @ defaults[[n]]} ], {n, Length @ defaults} ] ] ]

makeDefaults[fname_Symbol, defaults_List] := With[{par = Table[Unique["$"], {Length @ defaults}]}, With[{set = Hold[# := #2] &[fname @@ (Pattern[#, _] & /@ par), fname @@ par]}, Do[ ReplacePart[set, {0 -> Identity, {1, 1, n} -> Null, {1, 2, n} -> defaults[[n]]}], {n, Length @ defaults} ] ] ]