package ppx_optional

ppx_optional - match statements for zero-alloc options

A ppx rewriter that rewrites simple match statements with an if then else expression.

Syntax

ppx_optional rewrites the extension match%optional in expressions. It requires that a module Optional_syntax is in scope, and that it has is_none and unsafe_value values.

For instance:

match%optional e with
| None -> none_expression
| Some x -> some_expression

becomes:

if Optional_syntax.is_none e then begin
   none_expression
end else begin
   let x = Optional_syntax.unsafe_value e in
   some_expression
end

Another example with multiple values and inline getting Optional_syntax in scope:

match%optional.Price_float.Option a, b with
| None, None -> expression_a
| Some a, None -> expression_b
| None, Some b -> expression_c
| Some a, Some b -> expression_d

Usage

This is normally used to safely access an optional value while avoiding allocation for immediate values (e.g. Immediate.{Char,Bool,Int}.Option, Fixed.Option, Price.Fixed.Option, etc...).