Subset preprocessor

sub process-module(Str:D $_ is copy --> Str:D) {

s:g/^^ "subset" \s+ (<:Lu><:L>*) \s+ '=' \s+ (.+?) \s+ "where" \s+ (.+?) \s* $$/&process-declaration(~$0, ~$1, ~$2)/;

s:g/^^ (. .) "subset" \s+ (<:Lu><:L>*) \s* $$/{$0 ~ process-export(~$1)}/;

$_;

}

sub process-declaration(Str:D $name, Str:D $type, Str:D $condition --> Str:D) {

qq:to/EOF/;

newtype $name = $name ($type)

{ctor-name $name} :: ($type) -> Maybe $name

{ctor-name $name} x

| ($condition) x = Just ($name x)

| otherwise = Nothing

{dtor-name $name} :: $name -> ($type)

{dtor-name $name} ($name x) = x

EOF

}

sub process-export(Str:D $name --> Str:D) {

qq:to/EOF/;

$name

, {ctor-name $name}

, {dtor-name $name}

EOF

}

sub ctor-name(Str:D $name --> Str:D) { $name.substr(0, 1).lc ~ $name.substr(1) }

sub dtor-name(Str:D $name --> Str:D) { "un$name" }

sub MAIN {

print process-module($=finish);

}

=finish

module Data.String.NonEmpty

( subset NonEmptyString

) where

import Data.Maybe (Maybe(..))

import Prelude

subset NonEmptyString = String where (_ /= "")