Custom operators

RiX supports statically declared, delimited infix operators. The delimiter is :<...>: and declarations live in a tagged comment before executable code:

##OPS##
:<o+>: Mediant :infix :additive :none
##OPS##

Mediant(a, b) -> a + b
value := 2 :<o+>: 3

Declaration fields are separated by whitespace and their order is irrelevant. Exactly one field must supply each meaning: operator spelling, callable target, fixity, precedence, and associativity. RiX supports :infix with :left, :right, or :none.

Named precedence bands include :assignment, :pipe, :arrow, :logical_or, :logical_and, :condition, :equality, :comparison, :interval, :conversion, :additive, :multiplicative, :power, :calculus, :postfix, and :property. :above or :below places an operator in the adjacent gap:

##OPS##
:<dot+>: DotAdd :infix :above :additive :left
##OPS##

A standalone declaration may target a system/plugin method explicitly:

##OPS##
:<o+>: .fractions.Mediant :infix :additive :none
##OPS##

Inside a plugin-owned operator file, the plugin is already known, so the short target Mediant means the method on that plugin object rather than a global function.

Preloading

The CLI reads an optional leading YAML doc-comment before parsing a script:

/**
plugins: [fraction-ops]
operator-files:
  - ./project.operators.rix
**/

Paths are resolved relative to the script. A plugin can contribute operator files from its own manifest:

operator-files: [fraction.operators.rix]

Loading with .Plugin.Load(...) inside a complete source file is too late to affect that file’s parse. Use the source header, a CLI preload option, or a plugin already loaded by the host. Runtime loading can make syntax available to later REPL submissions.

For an interactive session, operator files can be supplied directly:

rix --operator-file=project.operators.rix
rix --preamble=project-preamble.rix

The default REPL preamble is cli-preamble.rix in the RiX configuration directory. Its YAML header can preload plugins and operator files, and its body can define functions and values used by the session. See Getting started.

Scope

There are no current plans for user-defined prefix, postfix, or n-ary custom operators. Prefix notation such as negation or square root is generally as clear as an ordinary function. Postfix notation has familiar special cases such as factorial, percent, transpose, and derivatives, but the visible :<...>: delimiter removes much of its ergonomic advantage. N-ary notation is usually mixfix syntax—conditionals, slicing, bounded sums, or “between … and …”—and requires a grammar template with several operand holes rather than an operator token. Functions, methods, containers, and existing RiX syntax cover those cases more clearly. Binary infix notation remains the intended custom operator extension point.

Custom operator declarations are static for a parse. Undeclared operators, conflicting declarations, duplicate fields, late ##OPS## blocks, and chains of :none operators without parentheses are errors.

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