Substitution and Expansion

proplists:substitute_aliases/2

Allows you to rename keys systematically, useful when your API needs to support both British and American spellings:

lfe> (proplists:substitute_aliases 
      '((color colour) (center centre))
      '((color red) (size large) (center middle)))
((colour red) (size large) (centre middle))

The aliases list consists of {OldKey, NewKey} pairs. If the same old key appears multiple times, only the first alias is used—first come, first served, as civilized society demands.

proplists:substitute_negations/2

A delightfully specific function that both renames keys and negates boolean values:

lfe> (proplists:substitute_negations
      '((no_color color) (disable_cache cache))
      '((no_color true) (timeout 5000) (disable_cache false)))
((color false) (timeout 5000) cache)

This handles the common pattern where options can be expressed in negative form (no_foo, disable_bar) and need to be normalized to positive form with inverted values. Note that {disable_cache, false} becomes just cache, because the double negative resolves to an affirmative shorthand.

proplists:expand/2

Expands property macros into their full forms, allowing you to define shorthand notations:

lfe> (proplists:expand
      '((debug ((verbose true) (log_level debug) (trace true))))
      '((timeout 5000) debug (retry 3)))
((timeout 5000) (verbose true) (log_level debug) (trace true) (retry 3))

The expansion list contains {Property, Expansion} pairs. When a property matches, it’s replaced by the expansion terms. If you want the original property preserved, include it in the expansion. Expansions are not recursive—once expanded, the terms are considered done.

proplists:normalize/2

Passes a proplist through a pipeline of transformations, allowing you to build complex normalization strategies:

lfe> (proplists:normalize
      '((timeout 5000) no_verbose (colour red))
      '((negations ((no_verbose verbose)))
        (aliases ((colour color)))
        (expand ((debug ((verbose true) (log_level debug)))))))
((timeout 5000) (verbose false) (color red))

The stages are processed in order, and the result is automatically compacted. Typical usage involves:

1. Negations first: Convert no_foo to {foo, false}
2. Aliases second: Normalize variant spellings
3. Expansions last: Expand shorthand to full options

This is the functional equivalent of data cleaning, where messy user input becomes pristine internal representation.