GHCi run commands that are not documented in Users Guide Documentation

Hi,

GHCi commands all begin with : and the command name may be abbreviated.\\ if you write : add to the command, for example:\\ ::l or ::r or ::set +m and so on, the command run\\ on the other hand :: do not run\\

Hope this help

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Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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Interesting:\\ From a little testing it seems that commands that begin with a letter can be run with ::command instead of :command\\ Some other commands like :! :{ : do not allow ::! ::{ ::\\ Oddly ::? is accepted.

Edit: On more review,

The :? for :def mentions that commands that start with :: refer to builtin commands.

:def <cmd> <expr>           define command :<cmd> (later defined command has
                               precedence, ::<cmd> is always a builtin command)

This doesn't seem to be documented in the manual as you've mentioned and it should be, the odd ones out are :! :{ :} : which don't have :: versions.

As hinted by the :? help text for :def <cmd> <expr> you can overwrite existing commands with :def!, eg:

> let date _ = Data.Time.getZonedTime >>= print >> return ""
> :def! load date
> :l
2019-04-13 19:06:29.169470598 CEST

So :load (or :l) no longer loads a file/module but returns the current date and time. If you now really want to load a file/module you still can do so by using the double colon ::load Foo.hs.

A short test shows, that :def (without the exclamation mark!) allows to overwrite existing commands. This is a bug, called bug-T13456-1!

The commands that can be exeuted with double colon (::) are those listed in ./ghc/UI.hs function ghciCommands. Except :? they all start with a letter.

Now the 3 so called exceptions:

:{ and :} don't need double colon versions, because it's impossible to overwrite them. Trying to do so result's in a syntax error!

:! is a bug: It's possible to define a macro :!. But it's not possible to use this macro. I call this bug bug-T13456-2

closed

reopened

assigned to @RolandSenn

mentioned in merge request !775 (merged)

Great job finding the bugs, @RolandSenn .

:! is a bug: It's possible to define a macro :!. But it's not possible to use this macro. I call this bug bug-T13456-2

We could fix this by one of these two: (1) disabling defining a ! macro (2) allowing ::!. I wonder which one would be better.

@osa1 My fix in !775 (merged) disables defining a ! macro. I don't really see any use case for this.

This reminds me of the language PL/I. This language had no reserved words. So one could define variables with names like IF, THEN or ELSE and write confusing statements like

IF IF THEN THEN ELSE ELSE;
IF ELSE THEN THEN ELSE IF;

changed milestone to %8.10.1

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!775 (merged) was merged into master with commit c7913f71

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