預設

Starts the default branch of an 選擇 or 比對 statement.

Aliases: default

Syntax: 預設 <block>

Category#

control-flow

Related#

• 選擇
• 比對

Examples#

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

Starts the default branch of an 選擇 or 比對 statement.

# =============================================================================
# 預設 — Starts the default branch of an 選擇 or 比對 statement.
# =============================================================================
#
# What this teaches:
#   • Default arm — `預設 <block>` is the catch-all branch in an `選擇`
#     or `比對` match expression
#   • Fallback handling — when no `分支` pattern matches, execution falls
#     through to the `預設` block
#
# Common mistakes:
#   • using `預設` with `比對 全部` — `全部` forbids catchall arms and requires listing every variant explicitly (SEM044)
#
# See also: 選擇, 比對
# =============================================================================

# 預設 — default 選擇 arm
#
# GRAMMAR:
#   defaultClause :← '預設' block
#
# EXPECTED OUTPUT:
#   Scalar stdout smoke (see body).
#
# BACKEND:
#   Cross-ref: 選擇/ceterum.fab.
#

main {
    const _ 標籤 ← "z"
    switch 標籤 {
        case "a" { print "a" }
        default { print "default" }
    }
}

Expected output:

default