6.20 Implicit Forms

8.12

6.20 Implicit Forms🔗ℹ

Rhombus parsing is driven by bindings even for forms that have no apparent name, such as a literal expression like 7 or square brackets like [1, 2, 3]. In those cases without an apparent name an implement form is used to give meaning to the term, whether in an expression position, binding position, or other kind of position. For positions that allow only prefix operators, such as definition positions, only prefix implicits are used. Here are all of the implicit forms:

#%literal — used for anything other than an identifier, keyword, operator, or compound form
#%parens — used for (…)
#%brackets — used for […]
#%braces — used for {…}
#%quotes — used for '…'
#%call — used as an infix form when a parsed form is followed immediately by a (…) term
#%index — used as an infix form when a parsed form is followed immediately by a […] term
#%comp — used as an infix form when a parsed form is followed immediately by a {…} term; this implicit form is not bound by rhombus
#%juxtapose — used as an infix form when a parsed form is followed immediately by a non-compound term; this implicit form is not bound by rhombus
#%block — used for a block formed with : (by itself as a would-be parsed term); this implicit form is not bound by rhombus
#%alts — used for a block formed with | (by itself as a would-be parsed term); this implicit form is not bound by rhombus
#%body — used by forms that contain a body sequence, such as block, the body of fun, and the result part of a match clause; the lexical context of the : or | that forms a block determines the #%body binding that is used

expression

#%literal literal

binding operator

#%literal literal

annotation

#%literal literal

repetition

#%literal literal

Produces the value literal as an expression or matches values that are == to literal as a binding; the annotation form reports an error that a literal is not allowed as an annotation. A literal also works as a repetition of depth 0, which can be useful for repeating a constant alongside a repetition of greater depth.

A literal is any individual term other than an identifier, keyword, operator, parenthesized term, bracketed term, braced term, quoted term, block, or alternatives.

> 7
7
> #%literal 7
7
> fun only_sevens(7): "yes"
> only_sevens(7)
"yes"
> only_sevens(8)
only_sevens: argument does not satisfy annotation
argument: 8
annotation: matching(7)

expression

#%parens (expr)

binding operator

#%parens (bind)

annotation

#%parens (annot)

Provided both normally and as meta.

Produces the same value as expr, same binding as bind, and so on. Multiple expression, bindings, etc., are disallowed.

> (1+2)
3
> #%parens (1+2)
3
> def (x) = 1+2
> x
3

expression

#%body:

body

...

Returns the result of the body block, which may include local definitions. The body sequence does not implicitly use #%body again.

1	Rhombus Essentials
2	Collections and Iteration
3	Syntax Objects and Macros
4	Classes and Interfaces
5	Static Information and Binding
6	Core Reference
7	Meta and Macros Reference
8	Rhombus Static by Default
9	Libraries
10	Naming Conventions

6.1	General Forms
6.2	Definitions
6.3	Namespaces
6.4	Import
6.5	Export
6.6	Functions
6.7	Operators
6.8	Classes and Interfaces
6.9	Veneers
6.10	Mutable Variables and Assignment
6.11	Repetitions
6.12	Block
6.13	Conditionals
6.14	Matching
6.15	Iteration
6.16	Recursion
6.17	Context Parameters
6.18	Exceptions
6.19	Continuations
6.20	Implicit Forms
6.21	Static and Dynamic Lookup
6.22	Modules and Submodules
6.23	Booleans
6.24	Numbers
6.25	Characters
6.26	Strings
6.27	Keywords
6.28	Symbols
6.29	Byte Strings
6.30	Lists
6.31	Pairs and Pair Lists
6.32	Mutable Lists
6.33	Arrays
6.34	Maps
6.35	Sets
6.36	Boxes
6.37	Indexables
6.38	Listables
6.39	Sequences
6.40	Appendables
6.41	Comparables
6.42	Paths
6.43	Source Locations
6.44	Void
6.45	Equality
6.46	Dot
6.47	Multiple Values
6.48	Annotations
6.49	Enumerations
6.50	Input and Output
6.51	Eval
6.52	Syntax Objects
6.53	Syntax Classes
6.54	Simple Expression Macros
6.55	Unit Testing