Expression Can Be Simplified 
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Expressions that are mathematically or logically redundant (e.g. identity or absorbing constants) should be simplified.
Avoid/prefer
| Expression to avoid | Prefer | Label (for simplifications) |
|---|---|---|
[] ++ X | X | list_append_left_empty |
X ++ [] | X | list_append_right_empty |
[] -- X | [] | list_subtract_from_empty |
X -- [] | X | list_subtract_empty |
X + 0 | X | add_zero_right |
X - 0 | X | subtract_zero |
0 - X | -X | subtract_from_zero |
X * 1 | X | multiply_by_one_right |
1 * X | X | multiply_by_one_left |
X div 1 | X | div_by_one |
X rem 1 | 0 | rem_by_one |
true andalso X | X | andalso_true |
false orelse X | X | orelse_false |
not true | false | not_true |
not false | true | not_false |
X band -1 | X | band_neg_one |
X bor 0 | X | bor_zero |
X bxor 0 | X | bxor_zero |
Rationale
Operations with identity or absorbing constants (e.g. X + 0, [] ++ X, true andalso X) have
well-defined outcomes that can be written more clearly by using the simplified form.
Simplifying improves readability and avoids redundant code.
This rule is separate from No Operator With Same Values,
which targets expressions like X op X where both operands are the same.
Options
simplifications :: [atom()]- List of simplification patterns to check. Omit a label to disable that pattern.
- Default: all of the following
- Labels:
list_append_left_empty,list_append_right_empty,list_subtract_from_empty,list_subtract_empty,add_zero_right,subtract_zero,subtract_from_zero,multiply_by_one_right,multiply_by_one_left,div_by_one,rem_by_one,andalso_true,orelse_false,not_true,not_false,band_neg_one,bor_zero,bxor_zero
Example configuration
{elvis_style, expression_can_be_simplified, #{
simplifications =>
[
list_append_left_empty,
list_append_right_empty,
list_subtract_from_empty,
list_subtract_empty,
add_zero_right,
subtract_zero,
subtract_from_zero,
multiply_by_one_right,
multiply_by_one_left,
div_by_one,
rem_by_one,
andalso_true,
orelse_false,
not_true,
not_false,
band_neg_one,
bor_zero,
bxor_zero
]
}}To enable only a subset (e.g. list and arithmetic simplifications):
{elvis_style, expression_can_be_simplified, #{
simplifications =>
[
list_append_left_empty,
list_append_right_empty,
list_subtract_empty,
add_zero_right,
subtract_zero,
multiply_by_one_right,
multiply_by_one_left
]
}}