渲染zh-Hans

discerne

Translation status: 简体中文 reader-locale proof. Code fences render through the zh-Hans pipeline; prose is canonical Latin.

Starts an exhaustive pattern match over a value or values.

Aliases: match

Syntax: discerne <subject> <block>

Category#

control-flow

Examples#

radix/corpus/discerne/discerne.fab (canonical · keyword)#

Starts an exhaustive pattern match over a value or values.

# =============================================================================
# discerne — Starts an exhaustive pattern match over a value or values.
# =============================================================================
#
# What this teaches:
#   • Exhaustive pattern matching — `discerne <value> { casu ... }` matches against all variants of a discretio (tagged union).
#   • Variant destructuring — `casu <Variant> fixum <field>, ...` destructures variant payload fields.
#   • Unit variants — variant without payload fields match by name alone.
#
# Common mistakes:
#   • Non-exhaustive match — omitting a variant from `discerne` without a `ceterum` catchall; every discretio variant must be covered (SEM040).
#
# See also: discretio, casu
# =============================================================================

# discerne — pattern matching on discretio values
#
# discerne <value> {
#     casu <Casus> { <body> }
#     casu <Casus> ut <alias> { <body> }
#     casu <Casus> fixum <bindings> { <body> }
#     casu <Casus> fixum <field> ut <alias> { <body> }
# }
#
# GRAMMAR:
#   discerneStmt :← 'discerne' expr '{' casuClause* '}'
#
# EXPECTED OUTPUT:
#   discerne exempla parata

# discretio — tagged union / enum declaration
union Condicio {
    Agens,
    Iners,
    Pendens
}

union Nuntius {
    Pulsus { int x, int y },
    Clavis { string clavis },
    Finis
}

# Simple casu matching on unit variants (no payload)
fn nomina(Condicio s) → string {
    match s {
        case Agens { return "agens" }
        case Iners { return "iners" }
        case Pendens { return "pendens" }
    }
}

# casu with fixum bindings destructures variant fields
fn tracta(Nuntius e) → null {
    match e {
        case Pulsus const x, y {
            print "pulsus: § §"(x, y)
        }
        case Clavis const clavis {
            print "clavis: §"(clavis)
        }
        case Finis {
            print "finis"
        }
    }
}

main {
    # nomina/tracta are defined for downstream exempla; smoke check only
    print "discerne exempla parata"
}

Expected output:

discerne exempla parata