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Lean can process input incrementally, and extract type information. This feature is useful for implementing "intelligent" support for Lean in editors such as Emacs. It provides a convenient way to access descriptions of functions, overloaded symbols, and typing information. We must use the option --server to enable this feature.

Commands

Lean implements a simple set of commands for loading files, extracting typing information, and "replacing" lines. The commands should be sent to the standard input.

Load file 

LOAD [file-name]

This command loads the Lean file named [file-name]. Lean will create a "snapshot" (aka backtracking point) after each command. Lean uses the "snapshots" to process incremental updates efficiently.

Visit file 

VISIT [file-name]

Lean can keep information about multiple files. This command sets [file-name] as the "current" file. The remaining commands are all with respect to the current file. If [file-name] has not been loaded yet, then this command will load it. Some of the remaining commands apply "changes" to the current file. The LOAD command can be used to discard all these changes, and enforce the content of the file stored in file system.

Synchronize

The following command can be used to make sure the front-end application and lean have the same "view". It resets the contents associated with current visited file/buffer.

SYNC [num]
line_1
...
line_num

Replace line 

REPLACE [line-number]
[new-line]

This command replaces the line [line-number] (in the current file) with [new-line]. Lean uses the snapshots to process the request efficiently. If [line-number] is greater than the total number of lines in the lean buffer, then empty lines are introduced. The lines are indexed from 1.

Insert line 

INSERT [line-number]
[new-line]

This command inserts [new-line] (in the current file) before line [line-number]. If [line-number] is greater than the total number of lines in the lean buffer, then empty lines are introduced. The lines are indexed from 1.

Remove line 

REMOVE [line-number]

Remove line [line-number] (in the current file). The lines are indexed from 1. If [line-number] is greater than the total number of lines in the lean buffer, then the command is ignored.

Extracting information 

INFO [line-number] [column-number]?

This command extracts typing information associated with line [line-number] (in the current file) and [column-number]. If [column-number] is not provided then (potentially) long information is not included. Lean produces a possible empty sequence of entries delimited by the lines -- BEGININFO and -- ENDINFO.

-- BEGININFO
[entries]*
-- ENDINFO

If the server is still busy processing a previously requested update, then it produces the output

-- BEGININFO
-- NAY
-- ENDINFO

where NAY stands for "not available yet".

A type information entry is of the form

-- TYPE|[line-number]|[column-number]
[type]
-- ACK

Information for overloaded operators and symbols is of the form

-- OVERLOAD|[line-number]|[column-number]
[overload-1]
--
...
--
[overload-n]
-- ACK

Information for synthesized placeholders is of the form

-- SYNTH|[line-number]|[column-number]
[synthesized-term]
-- ACK

The following two information entries provide information for Lean keywords/symbols and identifiers.

-- SYMBOL|[line-number]|[column-number]
[symbol]
-- ACK
-- IDENTIFIER|[line-number]|[column-number]
[fully-qualified-name]
-- ACK

Information about introduced coercions is of the form

-- COERCION|[line-number]|[column-number]
[coercion-application]
--
[result-type]
-- ACK

When [column-number] is provided in the INFO command, the type of terms surrounded by () is also included. The ouput has the form

-- EXTRA_TYPE|[line-number]|[column-number]
[term]
--
[type]
-- ACK

Here is an example of output produced by Lean

-- BEGININFO
-- TYPE|15|38
num
-- ACK
-- TYPE|15|40
num → num → Prop
-- ACK
-- OVERLOAD|15|42
f
--
foo.f
-- ACK
-- TYPE|15|42
num → num
-- ACK
-- TYPE|15|44
num
-- ACK
-- IDENTIFIER|15|42
foo.f
-- ACK
-- ENDINFO

Check line

As described above, several commands can be used to apply modifications to opened/visited files. These modification reflect modifications performed by the text editor. The command CHECK can be used to double check whether the text editor and Lean have the "same view" of the current file + modifications.

The following commands returns -- OK if the line [line-number] in the current file is [line]. It returns -- MISMATCH line out of range, if [line-number] is too big, and -- MISMATCH expected [lean-line] when there is a mismatch, and Lean expects [line-number] to be [lean-line].

-- CHECK [line-number]
[line]

Set configuration option

The command

-- SET
[option-name] [value]

sets a Lean options, [option-name] must be a valid Lean option. Any option that can be set using the command set_option in a '.lean' file is supported.

This command produces the output

-- BEGINSET
[error]?
-- ENDSET

where the line [error]? is printed if there are errors parsing the SET command (e.g., invalid option name).

Here is an example that forces the Lean pretty printer to display implicit arguments.

-- SET
pp.implicit true

Eval

The following command evaluates a Lean command. It has the effect of evaluating a command in the end of the current file

-- EVAL
[command]

This command produces the output

-- BEGINEVAL
[error]/[output]
-- ENDEVAL

Here is an example that executes the check command to obtain the type of Prop.

-- EVAL
check Prop

If the server is still busy processing a previously requested update, then it produces the output

-- BEGINEVAL
-- NAY
-- ENDEVAL

Wait

The following command is for debugging purposes. It blocks the server until all pending information has been computed.

WAIT

Options

The command OPTIONS display all configuration options available in Lean. It has the form

OPTIONS

The output is a sequence of entries

-- BEGINOPTIONS
[entry]*
-- ENDOPTIONS

where each entry is of the form

-- [name]|[kind]|[default-value]|[description]

The available kinds are: Bool, Int, Unsigned Int, Double, String, and S-Expressions.

Find pattern

Given a sequence of characters, the command FINDP uses string fuzzy matching to find declarations in the environment. The procedure uses [Bitap algorithm](http://en.wikipedia.org/wiki/Bitap_algorithm). The approximate match is defined in terms of [Levenshtein distance](http://en.wikipedia.org/wiki/Levenshtein_distance). The matches are sorted based on this distance.

FINDP [line-number]
[pattern]

The line number [line-number] is used to select the environment object that will be used to perform the search. Only declarations in the environment are considered by FINDP. The output has the following form

-- BEGINFINDP [NAY]? [STALE]?
[entries]*
-- ENDFINDP

The modifier NAY is included when the environment object for the given line is not available yet. The modifier STALE is included to indicate that an environment object is being used, but it does not contain the latest changes.

The entries are of the form

[name]|[type]

The types are printed without using line breaks. The command FINDP is mainly used to implement auto-completion.

Find declarations for "placeholder/goal"

A declaration may contain placeholders/goals _. Some of these placeholders are instantiated automatically by Lean. Others, must be manually filled by the user. The command FINDG generates a sequence of declarations that may be used to "fill" a particular placeholder. This command is only available if the declaration containing _ is type correct, and lean "knows" what is the expected type for _.

FINDG [line-number] [column-number]
[filters]*

The character at the given [line-number] and [column-number] must be a _. The command also accepts a sequence of filters of the form +[id_1] and -[id_2]. Lean will only consider declarations whose name contains id_1 and does not contain id_2. Here is an example:

FINDG 48 10
+intro -and -elim

For the command above, lean will print any declaration whose resultant type matches the type expected by _, and whose name contains intro but does not contain and and elim. Lean does not display "trivial" matches. We say a match is trivial if the resultant type of a declaration matches anything.

The output produced by FINDG uses the same format used by FINDP.