∪

Inline value unions and discerne on discretio variants.

Syntax: typus <name> = <type> ∪ <type>

Category

type

Related

• typus
• discerne
• discretio

Examples

examples/corpus/unio/unio.fab (canonical · operator-group)

Inline value unions and discerne on discretio variants.

# Inline value unions and discerne on discretio
#
# typus Valor = numerus ∪ textus models a non-nullable ad-hoc union.
# discretio + discerne handles tagged variants with payloads.
#
# GRAMMAR:
#   typeAlias :← 'typus' ident '=' typeExpr ('∪' typeExpr)*
#   discerne  :← 'discerne' expr '{' 'casu' variant pattern block ... '}'
#
# EXPECTED OUTPUT:
#   42, "salve", "n: 7", "t: faber"
#
# BACKEND: Inline-union `discerne` enum lowering gap on Rust (whitelist: unio/unio.fab).

typus Valor = numerus ∪ textus

discretio Forma {
    Numerus { numerus v },
    Textus { textus v }
}

functio describe(Forma f) → textus {
    discerne f {
        casu Numerus fixum v { redde "n: §"(v) }
        casu Textus fixum v { redde "t: §"(v) }
    }
}

incipit {
    # --- Ad-hoc inline union values ---

    fixum Valor a ← 42
    fixum Valor b ← "salve"
    nota a
    nota b

    # --- Tagged discretio variants via finge ---

    nota describe(finge Numerus { v = 7 } ∷ Forma)
    nota describe(finge Textus { v = "faber" } ∷ Forma)
}

Expected output:

42
salve
n: 7
t: faber