# Version-2–4−0

  ------------------------------------------------------------------------
— Release notes for Agda 2 version 2.4.0
------------------------------------------------------------------------

Important changes since 2.3.2:

Installation and Infrastructure
===============================

* A new module called Agda.Primitive has been introduced. This module
is available to all users, even if the standard library is not used.
Currently the module contains level primitives and their
representation in Haskell when compiling with MAlonzo:

infixl 6 _⊔_

postulate
Level : Set
lzero : Level
lsuc  : (ℓ : Level) → Level
_⊔_   : (ℓ₁ ℓ₂ : Level) → Level

{-# COMPILED_TYPE Level ()      #-}
{-# COMPILED lzero ()           #-}
{-# COMPILED lsuc  (\_ → ())   #-}
{-# COMPILED _⊔_   (\_ _ → ()) #-}

{-# BUILTIN LEVEL     Level  #-}
{-# BUILTIN LEVELZERO lzero  #-}
{-# BUILTIN LEVELSUC  lsuc   #-}
{-# BUILTIN LEVELMAX  _⊔_    #-}

To bring these declarations into scope you can use a declaration
like the following one:

open import Agda.Primitive using (Level; lzero; lsuc; _⊔_)

The standard library reexports these primitives (using the names
zero and suc instead of lzero and lsuc) from the Level module.

Existing developments using universe polymorphism might now trigger
the following error message:

Duplicate binding for built-in thing LEVEL, previous binding to
.Agda.Primitive.Level

To fix this problem, please remove the duplicate bindings.

Technical details (perhaps relevant to those who build Agda
packages):

The include path now always contains a directory <DATADIR>/lib/prim,
and this directory is supposed to contain a subdirectory Agda
containing a file Primitive.agda.

The standard location of <DATADIR> is system- and
installation-specific.  E.g., in a cabal —user installation of
Agda-2.3.4 on a standard single-ghc Linux system it would be
\$HOME/.cabal/share/Agda-2.3.4 or something similar.

The location of the <DATADIR> directory can be configured at
compile-time using Cabal flags (--datadir and —datasubdir).
The location can also be set at run-time, using the Agda_datadir
environment variable.

Pragmas and Options
===================

* Pragma NO_TERMINATION_CHECK placed within a mutual block is now
applied to the whole mutual block (rather than being discarded
silently).  Adding to the uses 1.−4. outlined in the release notes
for 2.3.2 we allow:

3a. Skipping an old-style mutual block: Somewhere within ‘mutual’
block before a type signature or first function clause.

mutual
{-# NO_TERMINATION_CHECK #-}
c : A
c = d

d : A
d = c

* New option —no-pattern-matching

Disables all forms of pattern matching (for the current file).
You can still import files that use pattern matching.

* New option -v profile:7

Prints some stats on which phases Agda spends how much time.
(Number might not be very reliable, due to garbage collection
interruptions, and maybe due to laziness of Haskell.)

* New option —no-sized-types

Option —sized-types is now default.
—no-sized-types will turn off an extra (inexpensive) analysis on
data types used for subtyping of sized types.

Language
========

TODO: Document quoteContext.

* Experimental feature: Varying arity.
Function clauses may now have different arity, e.g.,

Sum : ℕ → Set
Sum 0       = ℕ
Sum (suc n) = ℕ → Sum n

sum : (n : ℕ) → ℕ → Sum n
sum 0       acc   = acc
sum (suc n) acc m = sum n (m + acc)

or,

T : Bool → Set
T true  = Bool
T false = Bool → Bool

f : (b : Bool) → T b
f false true  = false
f false false = true
f true = true

This feature is experimental.  Yet unsupported:
* Varying arity and ‘with’.
* Compilation of functions with varying arity to Haskell, JS, or Epic.

* Experimental feature: copatterns.  (Activated with option —copatterns)

We can now define a record by explaining what happens if you project
the record.  For instance:

{-# OPTIONS —copatterns #-}

record _×_ (A B : Set) : Set where
constructor _,_
field
fst : A
snd : B
open _×_

pair : {A B : Set} → A → B → A × B
fst (pair a b) = a
snd (pair a b) = b

swap : {A B : Set} → A × B → B × A
fst (swap p) = snd p
snd (swap p) = fst p

swap3 : {A B C : Set} → A × (B × C) → C × (B × A)
fst (swap3 t)       = snd (snd t)
fst (snd (swap3 t)) = fst (snd t)
snd (snd (swap3 t)) = fst t

Taking a projection on the left hand side (lhs) is called a
projection pattern, applying to a pattern is called an application
pattern.  (Alternative terms: projection/application copattern.)

In the first example, the symbol ‘pair’, if applied to variable
patterns a and b and then projected via fst, reduces to a.
‘pair’ by itself does not reduce.

A typical application are coinductive records such as streams:

record Stream (A : Set) : Set where
coinductive
field
tail : Stream A
open Stream

repeat : {A : Set} (a : A) → Stream A
tail (repeat a) = repeat a

Again, ‘repeat a’ by itself will not reduce, but you can take
a projection (head or tail) and then it will reduce to the
respective rhs.  This way, we get the lazy reduction behavior
necessary to avoid looping corecursive programs.

Application patterns do not need to be trivial (i.e., variable
patterns), if we mix with projection patterns.  E.g., we can have

nats : Nat → Stream Nat
tail (nats zero) = nats zero
head (nats (suc x)) = x
tail (nats (suc x)) = nats x

Here is an example (not involving coinduction) which demostrates
records with fields of function type:

record State (S A : Set) : Set where
constructor state
field
runState : S → A × S
open State

record Monad (M : Set → Set) : Set1 where
field
return : {A : Set}   → A → M A
_>>=_  : {A B : Set} → M A → (A → M B) → M B

— State is an instance of Monad
— Demonstrates the interleaving of projection and application patterns

let a , s₁ = runState m s₀
in  runState (k a) s₁

module MonadLawsForState {S : Set} where

leftId : {A B : Set}(a : A)(k : A → State S B) →
(return a >>= k) ≡ k a
leftId a k = refl

rightId : {A B : Set}(m : State S A) →
(m >>= return) ≡ m
rightId m = refl

assoc : {A B C : Set}(m : State S A)(k : A → State S B)(l : B → State S C) →
((m >>= k) >>= l) ≡ (m >>= λ a → (k a >>= l))
assoc m k l = refl

Copatterns are yet experimental and the following does not work:

* Copatterns and ‘with’ clauses.

* Compilation of copatterns to Haskell, JS, or Epic.

* Projections generated by
open R {{…}}
are not handled properly on lhss yet.

* Conversion checking is slower in the presence of copatterns,
since stuck definitions of record type do no longer count
as neutral, since they can become unstuck by applying a projection.
Thus, comparing two neutrals currently requires comparing all
they projections, which repeats a lot of work.

* Top-level module no longer required.

The top-level module can be omitted from an Agda file. The module name is
then inferred from the file name by dropping the path and the .agda
extension. So, a module defined in /A/B/C.agda would get the name C.

You can also suppress only the module name of the top-level module by writing

module _ where

This works also for parameterised modules.

* Module parameters are now always hidden arguments in projections.
For instance:

module M (A : Set) where

record Prod (B : Set) : Set where
constructor _,_
field
fst : A
snd : B
open Prod public

open M

Now, the types of fst and snd are

fst : {A : Set}{B : Set} → Prod A B → A
snd : {A : Set}{B : Set} → Prod A B → B

Until 2.3.2, they were

fst : (A : Set){B : Set} → Prod A B → A
snd : (A : Set){B : Set} → Prod A B → B

This change is a step towards symmetry of constructors and projections.
(Constructors always took the module parameters as hidden arguments).

* Telescoping lets: Local bindings are now accepted in telescopes
of modules, function types, and lambda-abstractions.

The syntax of telescopes as been extended to support ‘let’:

id : (let ★ = Set) (A : ★) → A → A
id A x = x

In particular one can now ‘open’ modules inside telescopes:

module Star where
★ : Set₁
★ = Set

module MEndo (let open Star) (A : ★) where
Endo : ★
Endo = A → A

Finally a shortcut is provided for opening modules:

module N (open Star) (A : ★) (open MEndo A) (f : Endo) where
…

The semantics of the latter is

module _ where
open Star
module _ (A : ★) where
open MEndo A
module N (f : Endo) where
…

The semantics of telescoping lets in function types and lambda
abstractions is just expanding them into ordinary lets.

* More liberal left-hand sides in lets [Issue 1028]:

You can now write left-hand sides with arguments also for let bindings
without a type signature. For instance,

let f x = suc x in f zero

Let bound functions still can’t do pattern matching though.

* Ambiguous names in patterns are now optimistically resolved in favor
of constructors. [Issue 822] In particular, the following succeeds now:

module M where

data D : Set₁ where
[_] : Set → D

postulate [_] : Set → Set

open M

Foo : _ → Set
Foo [ A ] = A

* Anonymous where-modules are opened public. [Issue 848]

<clauses>
f args = rhs
module _ telescope where
body
<more clauses>

means the following (not proper Agda code, since you cannot put a
module in-between clauses)

<clauses>
module _ {arg-telescope} telescope where
body

f args = rhs
<more clauses>

Example:

A : Set1
A = B module _ where
B : Set1
B = Set

C : Set1
C = B

* Builtin ZERO and SUC have been merged with NATURAL.

When binding the NATURAL builtin, ZERO and SUC are bound to the appropriate
constructors automatically. This means that instead of writing

{-# BUILTIN NATURAL Nat #-}
{-# BUILTIN ZERO zero #-}
{-# BUILTIN SUC suc #-}

you just write

{-# BUILTIN NATURAL Nat #-}

* Pattern synonym can now have implicit arguments. [Issue 860]

For example,

pattern tail=_ {x} xs = x ∷ xs

len : ∀ Ā → List A → Nat
len []         = 0
len (tail= xs) = 1 + len xs

* Syntax declarations can now have implicit arguments. [Issue 400]

For example

id : ∀ ā{A : Set a} → A → A
id x = x

syntax id Ā x = x ∈ A

* Minor syntax changes

* -} is now parsed as end-comment even if no comment was begun.
As a consequence, the following definition gives a parse error

f : {A- : Set} → Set
f {A-} = A-

because Agda now sees ID(f) LBRACE ID(A) END-COMMENT, and no
longer ID(f) LBRACE ID(A-) RBRACE.

The rational is that the previous lexing was to context-sensitive,
attempting to comment-out f using {- and -} lead to a parse error.

* Fixities (binding strengths) can now be negative numbers as
well. [Issue 1109]

infix −1 _myop_

* Postulates are now allowed in mutual blocks. [Issue 977]

* Empty where blocks are now allowed. [Issue 947]

* Pattern synonyms are now allowed in parameterised modules. [Issue 941]

* Empty hiding and renaming lists in module directives are now allowed.

* Module directives using, hiding, renaming and public can now appear in
arbitrary order. Multiple using/hiding/renaming directives are allowed, but
you still cannot have both using and hiding (because that doesn’t make
sense). [Issue 493]

Goal and error display
======================

* The error message “Refuse to construct infinite term” has been
removed, instead one gets unsolved meta variables.  Reason: the
error was thrown over-eagerly. [Issue 795]

* If an interactive case split fails with message

Since goal is solved, further case distinction is not supported;

then the associated interaction meta is assigned to a solution.
Press C-c C-= (Show constraints) to view the solution and C-c C-s
(Solve constraints) to apply it. [Issue 289]

Type checking
=============

* [ issue 376 ] Implemented expansion of bound record variables during meta assignment.
Now Agda can solve for metas X that are applied to projected variables, e.g.:

X (fst z) (snd z) = z

X (fst z)         = fst z

Technically, this is realized by substituting (x , y) for z with fresh
bound variables x and y.  Here the full code for the examples:

record Sigma (A : Set)(B : A → Set) : Set where
constructor _,_
field
fst : A
snd : B fst
open Sigma

test : (A : Set) (B : A → Set) →
let X : (x : A) (y : B x) → Sigma A B
X = _
in  (z : Sigma A B) → X (fst z) (snd z) ≡ z
test A B z = refl

test’ : (A : Set) (B : A → Set) →
let X : A → A
X = _
in  (z : Sigma A B) → X (fst z) ≡ fst z
test’ A B z = refl

The fresh bound variables are named fst(z) and snd(z) and can appear
in error messages, e.g.:

fail : (A : Set) (B : A → Set) →
let X : A → Sigma A B
X = _
in  (z : Sigma A B) → X (fst z) ≡ z
fail A B z = refl

results in error:

Cannot instantiate the metavariable _7 to solution fst(z) , snd(z)
since it contains the variable snd(z) which is not in scope of the
metavariable or irrelevant in the metavariable but relevant in the
solution
when checking that the expression refl has type _7 A B (fst z) ≡ z

* Dependent record types and definitions by copatterns require
reduction with previous function clauses while checking the
current clause. [Issue 907]

For a simple example, consider

test : ∀ Ā → Σ Nat λ n → Vec A n
proj₁ test = zero
proj₂ test = []

For the second clause, the lhs and rhs are typed as

proj₂ test : Vec A (proj₁ test)
[]         : Vec A zero

In order for these types to match, we have to reduce the lhs type
with the first function clause.

Note that termination checking comes after type checking, so be
careful to avoid non-termination!  Otherwise, the type checker
might get into an infinite loop.

* The implementation of the primitive primTrustMe has changed.
It now only reduces to REFL if the two arguments x and y have
the same computational normal form.  Before, it reduced when
x and y were definitionally equal, which included type-directed
equality laws such as eta-equality.  Yet because reduction is
untyped, calling conversion from reduction lead to Agda crashes
[Issue 882].

The amended description of primTrustMe is (cf. release notes for 2.2.6):

primTrustMe : {A : Set} {x y : A} → x ≡ y

Here _≡_ is the builtin equality (see BUILTIN hooks for equality,
above).

If x and y have the same computational normal form, then
primTrustMe {x = x} {y = y} reduces to refl.

A note on primTrustMe’s runtime behavior:
The MAlonzo compiler replaces all uses of primTrustMe with the
REFL builtin, without any check for definitional equality. Incorrect
uses of primTrustMe can potentially lead to segfaults or similar
problems of the compiled code.

* Implicit patterns of record type are now only eta-expanded if there
is a record constructor. [Issues 473, 635]

data D : Set where
d : D

data P : D → Set where
p : P d

record Rc : Set where
constructor c
field f : D

works : {r : Rc} → P (Rc.f r) → Set
works p = D

This works since the implicit pattern {r} is eta-expanded to
{c x} which allows the type of p to reduce to P x and x to be
unified with d.  The corresponding explicit version is:

works’ : (r : Rc) → P (Rc.f r) → Set
works’ (c .d) p = D

However, if the record constructor is removed, the same example will
fail:

record R : Set where
field f : D

fails : {r : R} → P (R.f r) → Set
fails p = D

— d != R.f r of type D
— when checking that the pattern p has type P (R.f r)

The error is justified since there is no pattern we could write down
for r.  It would have to look like

record { f = .d }

but anonymous record patterns are not part of the language.

* Absurd lambdas at different source locations are no longer
different. [Issue 857]
In particular, the following code type-checks now:

absurd-equality : _≡_ {A = ⊥ → ⊥} (λ()) λ()
absurd-equality = refl

Which is a good thing!

* Printing of named implicit function types.

When printing terms in a context with bound variables Agda renames new
bindings to avoid clashes with the previously bound names. For instance, if A
is in scope, the type (A : Set) → A is printed as (A₁ : Set) → A₁. However,
for implicit function types the name of the binding matters, since it can be
used when giving implicit arguments.

For this situation, the following new syntax has been introduced:
{x = y : A} → B is an implicit function type whose bound variable (in scope
in B) is y, but where the name of the argument is x for the purposes of
giving it explicitly. For instance, with A in scope, the type {A : Set} → A
is now printed as {A = A₁ : Set} → A₁.

This syntax is only used when printing and is currently not being parsed.

* Changed the semantics of —without-K. [Issue 712, Issue 865, Issue 1025]

New specification of —without-K:

When —without-K is enabled, the unification of indices for pattern matching
is restricted in two ways:

1. Reflexive equations of the form x == x are no longer solved, instead Agda
gives an error when such an equation is encountered.

2. When unifying two same-headed constructor forms ‘c us’ and ‘c vs’ of type
‘D pars ixs’, the datatype indices ixs (but not the parameters) have to
be *self-unifiable*, i.e. unification of ixs with itself should succeed
positively. This is a nontrivial requirement because of point 1.

Examples:

* The J rule is accepted.

J : {A : Set} (P : {x y : A} → x ≡ y → Set) →
(∀ x → P (refl x)) →
∀ {x y} (x≡y : x ≡ y) → P x≡y
J P p (refl x) = p x

This definition is accepted since unification of x with y doesn’t require
deletion or injectivity.

* The K rule is rejected.

K : {A : Set} (P : {x : A} → x ≡ x → Set) →
(∀ x → P (refl {x = x})) →
∀ {x} (x≡x : x ≡ x) → P x≡x
K P p refl = p _

Definition is rejected with the following error:

Cannot eliminate reflexive equation x = x of type A because K has
been disabled.
when checking that the pattern refl has type x ≡ x

* Symmetry of the new criterion.

test₁ : {k l m : ℕ} → k + l ≡ m → ℕ
test₁ refl = zero

test₂ : {k l m : ℕ} → k ≡ l + m → ℕ
test₂ refl = zero

Both versions are now accepted (previously only the first one was).

* Handling of parameters.

cons-injective : {A : Set} (x y : A) → (x ∷ []) ≡ (y ∷ []) → x ≡ y
cons-injective x .x refl = refl

Parameters are not unified, so they are ignored by the new criterion.

* A larger example: antisymmetry of ≤.

data _≤_ : ℕ → ℕ → Set where
lz : (n : ℕ) → zero ≤ n
ls : (m n : ℕ) → m ≤ n → suc m ≤ suc n

≤-antisym : (m n : ℕ) → m ≤ n → n ≤ m → m ≡ n
≤-antisym .zero    .zero    (lz .zero) (lz .zero)   = refl
≤-antisym .(suc m) .(suc n) (ls m n p) (ls .n .m q) =
cong suc (≤-antisym m n p q)

* [ Issue 1025 ]

postulate mySpace : Set
postulate myPoint : mySpace

data Foo : myPoint ≡ myPoint → Set where
foo : Foo refl

test : (i : foo ≡ foo) → i ≡ refl
test refl = {!!}

When applying injectivity to the equation “foo ≡ foo” of type “Foo refl”,
it is checked that the index refl of type “myPoint ≡ myPoint” is
self-unifiable. The equation “refl ≡ refl” again requires injectivity, so
now the index myPoint is checked for self-unifiability, hence the error:

Cannot eliminate reflexive equation myPoint = myPoint of type
mySpace because K has been disabled.
when checking that the pattern refl has type foo ≡ foo

Termination checking
====================

* A buggy facility coined “matrix-shaped orders” that supported
uncurried functions (which take tuples of arguments instead of one
argument after another) has been removed from the termination
checker. [Issue 787]

* Definitions which fail the termination checker are not unfolded any
longer to avoid loops or stack overflows in Agda.  However, the
termination checker for a mutual block is only invoked after
type-checking, so there can still be loops if you define a
non-terminating function.  But termination checking now happens
before the other supplementary checks: positivity, polarity,
injectivity and projection-likeness.
Note that with the pragma {-# NO_TERMINATION_CHECK #-} you can make
Agda treat any function as terminating.

* Termination checking of functions defined by ‘with’ has been improved.

Cases which previously required —termination-depth
to pass the termination checker (due to use of ‘with’) no longer
need the flag. For example

merge : List A → List A → List A
merge [] ys = ys
merge xs [] = xs
merge (x ∷ xs) (y ∷ ys) with x ≤ y
merge (x ∷ xs) (y ∷ ys)    | false = y ∷ merge (x ∷ xs) ys
merge (x ∷ xs) (y ∷ ys)    | true  = x ∷ merge xs (y ∷ ys)

This failed to termination check previously, since the ‘with’ expands to an
auxiliary function merge-aux:

merge-aux x y xs ys false = y ∷ merge (x ∷ xs) ys
merge-aux x y xs ys true  = x ∷ merge xs (y ∷ ys)

This function makes a call to merge in which the size of one of the arguments
is increasing. To make this pass the termination checker now inlines the
definition of merge-aux before checking, thus effectively termination
checking the original source program.

As a result of this transformation doing ‘with’ on a variable no longer
preserves termination. For instance, this does not termination check:

… | zero  = zero
… | suc m = bad m

* The performance of the termination checker has been improved.  For
higher —termination-depth the improvement is significant.
While the default —termination-depth is still 1, checking with
higher —termination-depth should now be feasible.

Compiler backends
=================

* The MAlonzo compiler backend now has support for compiling modules
that are not full programs (i.e. don’t have a main function). The
goal is that you can write part of a program in Agda and the rest in
following features were added for this reason:

* A new command-line option —compile-no-main: the command

agda —compile-no-main Test.agda

will compile Test.agda and all its dependencies to Haskell and
compile the resulting Haskell files with —make, but (unlike
—compile) not tell GHC to treat Test.hs as the main module. This
type of compilation can be invoked from emacs by customizing the
agda2-backend variable to value MAlonzoNoMain and then calling
“C-c C-x C-c” as before.

* A new pragma COMPILED_EXPORT was added as part of the MAlonzo FFI.
If we have an agda file containing the following:

module A.B where

test : SomeType
test = someImplementation

then test will be compiled to a Haskell function called
someHaskellId in module MAlonzo.Code.A.B that can be invoked from
other Haskell code. Its type will be translated according to the
normal MAlonzo rules.

Tools
=====

Emacs mode
----------

* A new goal command “Helper Function Type” (C-c C-h) has been added.

If you write an application of an undefined function in a goal, the Helper
Function Type command will print the type that the function needs to have in
order for it to fit the goal. The type is also added to the Emacs kill-ring
and can be pasted into the buffer using C-y.

The application must be of the form “f args” where f is the name of the
helper function you want to create. The arguments can use all the normal
features like named implicits or instance arguments.

Example:

Here’s a start on a naive reverse on vectors:

reverse : ∀ {A n} → Vec A n → Vec A n
reverse [] = []
reverse (x ∷ xs) = {!snoc (reverse xs) x!}

Calling C-c C-h in the goal prints

snoc : ∀ Ā {n} → Vec A n → A → Vec A (suc n)

* A new command “Explain why a particular name is in scope” (C-c C-w) has been

This command can be called from a goal or from the top-level and will as the
name suggests explain why a particular name is in scope.

For each definition or module that the given name can refer to a trace is
printed of all open statements and module applications leading back to the
original definition of the name.

For example, given

module A (X : Set₁) where
data Foo : Set where
mkFoo : Foo
module B (Y : Set₁) where
open A Y public
module C = B Set
open C

Calling C-c C-w on mkFoo at the top-level prints

mkFoo is in scope as
* a constructor Issue207.C._.Foo.mkFoo brought into scope by
- the opening of C at Issue207.agda:13,6–7
- the application of B at Issue207.agda:11,12–13
- the application of A at Issue207.agda:9,8–9
- its definition at Issue207.agda:6,5–10

This command is useful if Agda complains about an ambiguous name and you need
to figure out how to hide the undesired interpretations.

* Improvements to the “make case” command (C-c C-c)

- One can now also split on hidden variables, using the name
(starting with .) with which they are printed.
Use C-c C-, to see all variables in context.

- Concerning the printing of generated clauses:

* Uses named implicit arguments to improve readability.

* Picks explicit occurrences over implicit ones when there is a choice of
binding site for a variable.

* Avoids binding variables in implicit positions by replacing dot patterns
that uses them by wildcards (._).

* Key bindings for lots of “mathematical” characters (examples: 𝐴𝑨𝒜𝓐𝔄)
have been added to the Agda input method.
Example: type \MiA\MIA\McA\MCA\MfA to get 𝐴𝑨𝒜𝓐𝔄.

Note: \McB does not exist in unicode (as well as others in that style),
but the \MC (bold) alphabet is complete.

* Key bindings for “blackboard bold” B (𝔹) and 0–9 (𝟘-𝟡) have been added
to the Agda input method (\bb and \b[0–9]).

* Key bindings for controlling simplification/normalisation:

[TODO: Simplification should be explained somewhere.]

Commands like “Goal type and context” (C-c C-,) could previously be
invoked in two ways. By default the output was normalised, but if a
prefix argument was used (for instance via C-u C-c C-,), then no
explicit normalisation was performed. Now there are three options:

* By default (C-c C-,) the output is simplified.

* If C-u is used exactly once (C-u C-c C-,), then the result is
neither (explicitly) normalised nor simplified.

* If C-u is used twice (C-u C-u C-c C-,), then the result is
normalised.

[TODO: As part of the release of Agda 2.3.4 the key binding page on
the wiki should be updated.]

LaTeX-backend
-------------

* Two new color scheme options were added to agda.sty:

\usepackage[bw]{agda}, which highlights in black and white;
\usepackage[conor]{agda}, which highlights using Conor’s colors.

The default (no options passed) is to use the standard colors.

* If agda.sty cannot be found by the latex environment, it is now
copied into the latex output directory (‘latex’ by default) instead
of the working directory. This means that the commands needed to
produce a PDF now is

agda —latex -i . <file>.lagda
cd latex
pdflatex <file>.tex

* The LaTeX-backend has been made more tool agnostic, in particular
XeLaTeX and LuaLaTeX should now work. Here is a small example
(test/latex-backend/succeed/UnicodeInput.lagda):

\documentclass{article}
\usepackage{agda}
\begin{document}

\begin{code}
data αβγδεζθικλμνξρστυφχψω : Set₁ where

postulate
→⇒⇛⇉⇄↦⇨↠⇀⇁ : Set
\end{code}

$∀X [ ∅ ∉ X ⇒ ∃f:X ⟶ ⋃ X\ ∀A ∈ X (f(A) ∈ A) ]$
\end{document}

Compiled as follows, it should produce a nice looking PDF (tested with
TeX Live 2012):

agda —latex <file>.lagda
cd latex
xelatex <file>.tex (or lualatex <file>.tex)

If symbols are missing or xelatex/lualatex complains about the font
missing, try setting a different font using:

\setmathfont{<math-font>}

Use the fc-list tool to list available fonts.

If the hyperref latex package is loaded before the agda package and
the links option is passed to the agda package, then the agda package
provides a function called \AgdaTarget. Identifiers which have been
declared targets, by the user, will become clickable hyperlinks in the
rest of the document. Here is a small example

\documentclass{article}
\usepackage{hyperref}
\begin{document}

\AgdaTarget{ℕ}
\AgdaTarget{zero}
\begin{code}
data ℕ : Set where
zero  : ℕ
suc   : ℕ → ℕ
\end{code}

See next page for how to define \AgdaFunction{two} (doesn’t turn into a
link because the target hasn’t been defined yet). We could do it

\newpage

\AgdaTarget{two}
\hypertarget{two}{}
\begin{code}
two : ℕ
two = suc (suc zero)
\end{code}

\AgdaInductiveConstructor{zero} is of type
\AgdaDatatype{ℕ}. \AgdaInductiveConstructor{suc} has not been defined to
be a target so it doesn’t turn into a link.

\newpage

Now that the target for \AgdaFunction{two} has been defined the link
works automatically.

\begin{code}
data Bool : Set where
true false : Bool
\end{code}

The AgdaTarget command takes a list as input, enabling several
targets to be specified as follows:

\AgdaTarget{if, then, else, if\_then\_else\_}
\begin{code}
if_then_else_ : {A : Set} → Bool → A → A → A
if true  then t else f = t
if false then t else f = f
\end{code}

\newpage

Mixfix identifier need their underscores escaped:
\AgdaFunction{if\_then\_else\_}.

\end{document}

The boarders around the links can be suppressed using hyperref’s