bricks-syntax- ...

Safe HaskellSafe





data Expression Source #


Expr'Var Var

A variable, such as x

Expr'Str Str'Dynamic

A string, quoted in the traditional form using a single double-quote (" ... ")

Expr'Str'Indented InStr

A string in "indented string" form, using two single-quotes ('' ... '')

Expr'List List

A list is an ordered collection of expressions.

Expr'Dict Dict

A dict is an unordered enumerated mapping from strings.

Expr'Dot Dot

A dot expression (named after the . character it contains) looks up the value at a particular key in a dict.

Expr'Lambda Lambda

A lambda expression x: y where x is the parameter.

Expr'Apply Apply

The application of a function to a single argument.

Expr'Let Let

A let-in expression consists of a list of variable bindings followed by an expression.


Show Expression Source #

This instance is designed for doctests and REPL experimentation. The format is designed to strike a balance in verbosity between the derived Show implementations (which are unwieldily long) and the Bricks language itself (which is quite terse but unsuitable for demonstrating the parser, as outputting a Bricks rendering of parse result wouldn't illumunate anyone's understanding of the AST that the Show instances are here to depict).


data Var Source #

A variable x, as in the lambda calculus sense, is in one of two positions:

  1. A binding, which may take a number of forms: - x: ... (Param'Name) - let x = ... ; in ... (LetBinding'Eq) - let inherit ( ... ) x; in ... (LetBinding'Inhherit)
  2. A contextual reference to a lambda head or let binding in which x is bound: - The expression x by itself - An inherit binding in a dict expression (DictBinding'Inherit'Var)


Variables are always written without quotes.

Unquoted strings are used for variables (Expr'Var) and places that bind variables (Lambda and Let).


Show Var Source # 


showsPrec :: Int -> Var -> ShowS #

show :: Var -> String #

showList :: [Var] -> ShowS #

Static strings

data Str'Static Source #

A fixed string value. We use the description "static" to mean the string may not contain antiquotation, in contrast with Str'Dynamic which can.

Dynamic strings

data Str'Dynamic Source #

A dynamic string is a quoted string expression, which may be a simple string like "hello" or a more complex string containing antiquotation like "Hello, my name is ${name}!". See Expr'Str.

We use the description "dynamic" to mean the string may contain antiquotation, in contrast with Str'Static which cannot.

This is the type of string expressions (Expr'Str).

String syntax

A string may be quoted either in the traditional form using a single double-quote (" ... "):


or in the "indented string" form using two single-quotes ('' ... ''):


Both of these examples reduce to the same value, because leading whitespace is stripped from indented strings.

Either may contain "antiquotation" (also known as "string interpolation") to conveniently concatenate string-valued variables into the string.

"Hello, my name is ${name}!"

Normal strings may contain the following escape sequences:

  • \\\
  • \""
  • \${${
  • \n → newline
  • \r → carriage return
  • \t → tab

The indented string form does not interpret any escape sequences.

str'dynamic'normalize :: Str'Dynamic -> Str'Dynamic Source #

Simplify a dynamic string by combining consecutive pieces of static text.


>>> :{
>>> str :: Text -> Str'1
>>> str x = Str'1'Literal $ Str'Static x Nothing
>>> var :: Text -> Str'1
>>> var x = Str'1'Antiquote . Expr'Var $
>>> Var (unquotedString'orThrow x) Nothing
>>> :}
>>> :{
>>> str'dynamic'normalize $ Str'Dynamic (Seq.fromList
>>> [str "a", str "b", var "x", var "y", str "c", str "d"]) Nothing
>>> :}
str ["ab", antiquote (var "x"), antiquote (var "y"), "cd"]

str'dynamic'to'static :: Str'Dynamic -> Maybe Str'Static Source #


>>> str'dynamic'to'static $ Str'Dynamic (Seq.fromList []) Nothing
Just ""
>>> a = Str'1'Literal (Str'Static "hi" Nothing)
>>> b = Str'1'Antiquote $ Expr'Var $ Var (unquotedString'orThrow "x") Nothing
>>> str'dynamic'to'static $ Str'Dynamic (Seq.fromList [ a ]) Nothing
Just "hi"
>>> str'dynamic'to'static $ Str'Dynamic (Seq.fromList [ a, b ]) Nothing

Indented string

data InStr Source #

An "indented string literal," delimited by two single-quotes ''.

This type of literal is called "indented" because the parser automatically removes leading whitespace from the string (inStr'dedent), which makes it convenient to use these literals for multi-line strings within an indented expression without the whitespace from indentation ending up as part of the string.


inStr'level :: InStr -> Natural Source #

Determine how many characters of whitespace to strip from an indented string.

inStr'dedent :: InStr -> InStr Source #

Determine the minimum indentation of any nonempty line, and remove that many space characters from the front of every line.

inStr'trim :: InStr -> InStr Source #

Remove any empty lines from the beginning or end of an indented string, and remove the newline from the final nonempty line.

Single line of an indented string

data InStr'1 Source #

One line of an InStr.






data List Source #

A list is an ordered collection.


A list expression (Expr'List) starts with [, ends with ], and contains any number of expressions in between.

The empty list:

[ ]

A list containing three variables:

[ a b c ]

Lambdas, function applications, let-in expressions, and with expressions must be parenthesized when in a list.

  (x: f x y)
  (g y)
  (let a = y; in f a a)
  (with d; f x a)



data Dict Source #

A dict is an unordered enumerated mapping from strings.


A dict expression (Expr'Dict) starts with { or rec {, ends with }, and contains any number of DictBindings in between.

The empty dict (with no bindings):

{ }

A dict with two bindings:

  a = "one";
  b = "one two";

By default, dict bindings cannot refer to each other. For that, you need the rec keyword to create a recursive dict.

rec {
  a = "one";
  b = "${a} two";

In either case, the order of the bindings does not matter.

The left-hand side of a dict binding may be a quoted string (in the traditional " ... " style, not the indented-string '' style), which make it possible for them to be strings that otherwise couldn't be expressed unquoted, such as strings containing spaces:

{ "a b" = "c"; }

The left-hand side of a dict may even be an arbitrary expression, using the ${ ... } form:

let x = "a b"; in { ${x} = "c"; }

Dicts also support the inherit keyword:

{ inherit a; inherit (x) c d; }

The previous expression is equivalent to:

{ a = a; c = x.c; d = x.d; }





Dict lookup

data Dot Source #

The dot function looks up a value (or a list of values) from a dict.


A dot expression is named after the . character it contains. a.b looks up value at key b in the dict a.

The examples in this section all reduce to "Z".

{ a = "Z"; }.a
let x = { a = "Z"; }; in x.a
{ x = { a = "Z"; }; }.x.a

The right-hand side of a dot may be a quoted string (in the traditional " ... " style, not the indented-string '' style):

{ a = "Z"; }."a"

The right-hand side of a dot may even be an arbitrary expression, using the ${ ... } form:

{ a = "Z"; }.${ let b = "a"; in b }


Show Dot Source # 


showsPrec :: Int -> Dot -> ShowS #

show :: Dot -> String #

showList :: [Dot] -> ShowS #

expression'applyDots Source #


:: Expression


-> [Expression]


-> Expression

Dot expression


data Lambda Source #

A function expressed as a lambda abstraction.


A lambda expression (Expr'Lambda) has the form x: y where x is the function parameter to bind in the function body y.

This is a function that turns a name into a greeting:

name: "Hello, ${name}!"

The function parameter can also be a dict pattern, which looks like this:

{ a, b, c ? "another" }: "Hello, ${a}, ${b}, and ${c}!"

That function accepts a dict and looks up the keys a, b, and c from it, applying the default value "another" to c if it is not present in the dict. Dict patterns therefore give us something that resembles functions with named parameters and default arguments.

By default, a lambda defined with a dict pattern fails to evaluate if the dict argument contains keys that are not listed in the pattern. To prevent it from failing, you can end the pattern with ... :

({ a, ... }: x) { a = "1"; b = "2"; }

Every function has a single parameter. If you need multiple parameters, you have to curry:

a: b: [ a b ]





Function parameters

data Param Source #

A parameter to a Lambda. All functions have a single parameter, but it's more complicated than that because it may also include dict destructuring.


Param'Name Var

A simple single-parameter function

Param'DictPattern DictPattern

Dict destructuring, which gives you something resembling multiple named parameters with default values

Param'Both Var DictPattern

Both a param name and a dict pattern, separated by the @ keyword


data DictPattern Source #

A type of function parameter (Param) that does dict destructuring.




data DictPattern'1 Source #

One item within a DictPattern.




Function application

data Apply Source #

The application of a function to a single argument.


An function application expression (Expr'Apply) looks like this:

f x

If a function has multiple (curried) parameters, you can chain them together like so:

f x y z





expression'applyArgs Source #


:: Expression


-> [Expression]


-> Expression

Function application


data Let Source #


A let-in expression (Expr'Let) looks like this:

  greet = x: "Hello, ${x}!";
  name = "Chris";
  greet name

Let bindings, like dict bindings, may also use the inherit keyword.

  d = { greet = x: "Hello, ${x}!"; name = "Chris"; }
  inherit (d) greet name;
  greet name

The previous example also demonstrates how the bindings in a let expression may refer to each other (much like a dict with the rec keyword). As with dicts, the order of the bindings does not matter.





Show Let Source # 


showsPrec :: Int -> Let -> ShowS #

show :: Let -> String #

showList :: [Let] -> ShowS #

data LetBinding Source #

A semicolon-terminated binding within the binding list of a Let expression.


LetBinding'Eq Var Expression

A binding with an equals sign, of the form x = y;

LetBinding'Inherit Expression (Seq Var)

A binding using the inherit keyword, of the form inherit (x) a b;