Emacs Mode

Agda programs are commonly edited using Emacs which is explained in this section. If you use Atom, please refer to the agda-mode on Atom.

Configuration

If you want to you can customise the Emacs mode. Just start Emacs and type the following:

M-x load-library RET agda2-mode RET
M-x customize-group RET agda2 RET

If you want some specific settings for the Emacs mode you can add them to agda2-mode-hook. For instance, if you do not want to use the Agda input method (for writing various symbols like ∀≥ℕ→π⟦⟧) you can add the following to your .emacs:

(add-hook 'agda2-mode-hook
          '(lambda ()
            ; If you do not want to use any input method:
            (deactivate-input-method)
            ; (In some versions of Emacs you should use
            ; inactivate-input-method instead of
            ; deactivate-input-method.)

Note that, on some systems, the Emacs mode changes the default font of the current frame in order to enable many Unicode symbols to be displayed. This only works if the right fonts are available, though. If you want to turn off this feature, then you should customise the agda2-fontset-name variable.

Keybindings

Notation for key combinations

The following notation is used when describing key combinations:

C-c
means hitting the c key while pressing the Ctrl key.
M-x
means hitting the x key while pressing the Meta key, which is called Alt on many systems. Alternatively one can type Escape followed by x (in separate key strokes).
RET
is the Enter, Return or key.
SPC
is the space bar.

Commands working with types can be prefixed with C-u to compute type without further normalisation and with C-u C-u to compute normalised types.

Global commands

C-c C-l
Load file
C-c C-x C-c
Compile file
C-c C-x C-q
Quit, kill the Agda process
C-c C-x C-r
Kill and restart the Agda process
C-c C-x C-a
Abort a command
C-c C-x C-d
Remove goals and highlighting (deactivate)
C-c C-x C-h
Toggle display of hidden arguments
C-c C-=
Show constraints
C-c C-s
Solve constraints
C-c C-?
Show all goals
C-c C-f
Move to next goal (forward)
C-c C-b
Move to previous goal (backwards)
C-c C-d
Infer (deduce) type
C-c C-o
Module contents
C-c C-z
Search Definitions in Scope
C-c C-n
Compute normal form
C-u C-c C-n
Compute normal form, ignoring abstract
C-u C-u C-c C-n
Compute and print normal form of show <expression>
C-c C-x M-;
Comment/uncomment rest of buffer
C-c C-x C-s
Switch to a different Agda version

Commands in context of a goal

Commands expecting input (for example which variable to case split) will either use the text inside the goal or ask the user for input.

C-c C-SPC
Give (fill goal)
C-c C-r
Refine. Partial give: makes new holes for missing arguments
C-c C-m
Elaborate and Give (fill goal with normalized expression). Takes the same C-u prefixes as C-c C-n.
C-c C-a
Automatic Proof Search (Auto)
C-c C-c
Case split
C-c C-h
Compute type of helper function and add type signature to kill ring (clipboard)
C-c C-t
Goal type
C-c C-e
Context (environment)
C-c C-d
Infer (deduce) type
C-c C-,
Goal type and context
C-c C-.
Goal type, context and inferred type
C-c C-;
Goal type, context and checked term
C-c C-o
Module contents
C-c C-n
Compute normal form
C-u C-c C-n
Compute normal form, ignoring abstract
C-u C-u C-c C-n
Compute and print normal form of show <expression>
C-c C-w
Why in scope, given a defined name returns how it was brought into scope and its definition

Other commands

TAB
Indent current line, cycles between points
S-TAB
Indent current line, cycles in opposite direction
M-.
Go to definition of identifier under point
Middle mouse button
Go to definition of identifier clicked on
M-*
Go back (Emacs < 25.1)
M-,
Go back (Emacs ≥ 25.1)

Unicode input

How can I write Unicode characters using Emacs?

The Agda Emacs mode comes with an input method for easily writing Unicode characters. Most Unicode character can be input by typing their corresponding TeX/LaTeX commands, eg. typing \lambda will input λ. Some characters have key bindings which have not been taken from TeX/LaTeX (typing \bN results in being inserted, for instance), but all bindings start with \.

To see all characters you can input using the Agda input method type M-x describe-input-method RET Agda or type M-x agda-input-show-translations RET RET (with some exceptions in certain versions of Emacs).

If you know the Unicode name of a character you can input it using M-x ucs-insert RET (which supports tab-completion) or C-x 8 RET. Example: Type C-x 8 RET not SPACE a SPACE sub TAB RET to insert the character “NOT A SUBSET OF” ().

(The Agda input method has one drawback: if you make a mistake while typing the name of a character, then you need to start all over again. If you find this terribly annoying, then you can use Abbrev mode instead. However, note that Abbrev mode cannot be used in the minibuffer, which is used to give input to many Agda and Emacs commands.)

The Agda input method can be customised via M-x customize-group RET agda-input.

OK, but how can I find out what to type to get the … character?

To find out how to input a specific character, eg from the standard library, position the cursor over the character and type M-x describe-char or C-u C-x =.

For instance, for I get the following:

            character: ∷ (displayed as ∷) (codepoint 8759, #o21067, #x2237)
    preferred charset: unicode (Unicode (ISO10646))
code point in charset: 0x2237
               script: symbol
               syntax: w      which means: word
             category: .:Base, c:Chinese
             to input: type "\::" with Agda input method
          buffer code: #xE2 #x88 #xB7
            file code: #xE2 #x88 #xB7 (encoded by coding system utf-8-unix)
              display: by this font (glyph code)
    x:-misc-fixed-medium-r-normal--20-200-75-75-c-100-iso10646-1 (#x2237)

Character code properties: customize what to show
  name: PROPORTION
  general-category: Sm (Symbol, Math)
  decomposition: (8759) ('∷')

There are text properties here:
  fontified            t

Here it says that I can type \:: to get a . If there is no “to input” line, then you can add a key binding to the Agda input method by using M-x customize-variable RET agda-input-user-translations.

Show me some commonly used characters

Many common characters have a shorter input sequence than the corresponding TeX command:

  • Arrows: \r- for . You can replace r with another direction: u, d, l. Eg. \d- for . Replace - with = or == to get a double and triple arrows.
  • Greek letters can be input by \G followed by the first character of the letters Latin name. Eg. \Gl will input λ while \GL will input Λ.
  • Negation: you can get the negated form of many characters by appending n to the name. Eg. while \ni inputs , \nin will input .
  • Subscript and superscript: you can input subscript or superscript forms by prepending the character with \_ (subscript) or \^ (superscript). Note that not all characters have a subscript or superscript counterpart in Unicode.

Some characters which were used in this documentation or which are commonly used in the standard library (sorted by hexadecimal code):

Hex code Character Short key-binding TeX command
00AC ¬   \neg
00D7 × \x \times
02E2 ˢ \^s  
03BB λ \Gl \lambda
041F П    
0432 в    
0435 е    
0438 и    
043C м    
0440 р    
0442 т    
1D62 \_i  
2032 \'1 \prime
207F \^n  
2081 \_1  
2082 \_2  
2083 \_3  
2084 \_4  
2096 \_k  
2098 \_m  
2099 \_n  
Hex code Character Short key-binding TeX command
2113   \ell
Hex code Character Short key-binding TeX command
2115 \bN \Bbb{N}
2191 \u \uparrow
2192 \r- \to
21A6 \r-| \mapsto
2200 \all \forall
2208   \in
220B   \ni
220C \nin  
2218 \o \circ
2237 \::  
223C \~ \sim
2248 \~~ \approx
2261 \== \equiv
2264 \<= \le
2284 \subn  
228E \u+ \uplus
2294 \lub  
22A2 \|- \vdash
22A4   \top
22A5   \bot
266D \b  
266F \#  
27E8 \<  
27E9 \>  
Hex code Character Short key-binding TeX command
2983 \{{  
2984 \}}  
2985 \((  
2986 \))  
Hex code Character Short key-binding TeX command
2C7C \_j  

Highlight

Clauses which do not hold definitionally (see Case trees) are highlighted in white smoke.