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elm

Why is a variable not immutable?

Why is varx not immutable in this code?

y = { g = 'a' }
z = { g = 1 }

varx = foo y

varx = foo z

Anybody knows? Thanks.

Solution

  • I guess that this code is executed in the Elm REPL. Immutable variables behave a little differently there. From the Beginning Elm book:

    https://elmprogramming.com/immutability.html

    The repl works a little differently. Whenever we reassign a different value to an existing constant, the repl essentially rebinds the constant to a new value. The rebinding process kills the constant and brings it back to life as if the constant was never pointing to any other value before.

    When compiling Elm code the ordinary way with Elm make, this code would lead to an error.