iif (etran v0.5.3)

Conditional expression functions

This module exports a parse transform and implements several condition-checking functions.

When using this as a parse transform, include the {parse_transform,iif} compiler option. In this case for given expressions A,B,C, and D the following code transforms will be done:

   iif(A, B)      -> case A of true -> B; _ -> undefined end
   iif(A, B, C)   -> case A of true -> B; _ -> C end
   iif(A,B,C,D)   -> case A of B -> C; _ -> D end
   nvl(A,B)       -> case A of false -> B; undefined -> B; [] -> B; _ -> A end
   nvl(A,B,C)     -> case A of false -> B; undefined -> B; [] -> B; _ -> C end

For debugging the AST of the resulting transform, use iif_debug command-line option:

   erlc -Diif_debug=1 ...    % Prints AST before the transform
   erlc -Diif_debug=2 ...    % Prints AST after the transform
   erlc -Diif_debug[=3] ...  % Prints AST before/after the transform

Alternative to using this module as a parse_transform, it implements several iif/3,4 exported functions that can be used without the transform.

Summary

Functions

format_ne(True, Fmt, Args)

Format if first argument is not empty

ife(Test, Value)

Return Value if first argument is one of: [], false, undefined. Otherwise return the value of the first argument.

ife(Value, Empty, NotEmpty)

Return Empty if first argument is one of: [], false, undefined. Otherwise, if NotEmpty is fun(), evaluate it, or if it's fun(Arg) evaluate it with Value argument.

ifne(Test, Value)

Return Value if first argument is not one of: [], false, undefined. Otherwise, if Value is fun(), evaluate it, or if it's fun(Arg) evaluate it with Test argument. If not empty

ifne(Value, NotEmpty, Empty)

Return NotEmpty if first argument is not one of: [], false, undefined. Otherwise, if NotEmpty is fun(), evaluate it, or if it's fun(Arg) evaluate it with Value argument.

iif(_, True, False)

Return True if first argument is true or return False if the first argument is one of: [], false, undefined.

iif(Value, Other, True, False)

Return True if first two arguments match

nvl(Value, IfNull)

Alias for ife/2

parse_transform(AST, Opts)

Parse transform to be used by providing {parse_transform, iif} option. Opts are compiler options passed from command line. E.g.