则

Introduces a compact statement consequent.

Aliases: ergo, therefore

Syntax: <head> 则 <statement>

Category#

control-flow

Related#

• 如果
• 返回
• 闭包
• ergo

Examples#

radix/corpus/operatores/control.fab (canonical · operator-group)#

Compact consequent after 如果/dum heads via 则, with ∴ reserved for closure bodies.

# =============================================================================
# 则 — Compact consequent after 如果/dum heads via 则, with ∴ reserved for closure bodies.
# =============================================================================
#
# What this teaches:
#   • Compact consequents — `则` follows `如果`, `否则如果`, `否则`, or `当` heads with a single consequent statement.
#   • Guard-return pattern — `如果 <cond> 则 返回 <value>` is a concise guard clause.
#
# Common mistakes:
#   • Using -> instead of → for function return types — Faber uses the Unicode arrow.
#
# See also: 如果, 返回, 闭包, 则
# =============================================================================

# operatores/control — 则 therefore consequent
#
# GRAMMAR:
#   consequentStmt :← ('如果' | '否则如果' | '否则' | '当') expr '则' stmt
#
# EXPECTED OUTPUT:
#   0, 100, 42
#
# BACKEND:
#   Cross-ref 如果/ergo-redde.fab for ergo-redde guard-return spelling.

fn clamp(int x) → int {
    if x ≺ 0 then return 0
    if x ≻ 100 then return 100
    return x
}

fn inveni(list<int> res, int quaesitum) → int ∪ none {
    for from res const item {
        if item ≡ quaesitum then return item
    }
    return null
}

main {
    print clamp(-5)
    print clamp(150)
    print inveni([10, 20, 42], 42)
}

Expected output:

0
100
42

radix/corpus/si/ergo-redde.fab (canonical · operator-group)#

Introduces a compact statement consequent.

# =============================================================================
# 则 — Introduces a compact statement consequent.
# =============================================================================
#
# What this teaches:
#   • Guard clauses — `如果 <cond> 则 返回 <expr>` provides a compact
#     one-liner for early returns
#   • `否则如果` and `否则` also accept `则` for chained guard expressions
#   • Demonstrates guard-return patterns, optional returns, and linear search
#
# Common mistakes:
#   • TODO: using `则` with a block instead of a single statement
#
# See also: 如果, 当, 闭包, 返回, 静默
# =============================================================================

# Si with 则 返回 syntax
#
# 如果 <conditio> 则 返回 <expressio>     -- guard return
# 否则如果 <conditio> 则 返回 <expressio>    -- else-if guard
# 否则 则 返回 <expressio>             -- else return
#
# GRAMMAR:
#   guardReturn :← ('如果' | '否则如果' | '否则') expr '则' '返回' expr
#
# EXPECTED OUTPUT:
#   Sign classes, division results, grades, and search hits.

fn classis(int x) → string {
    if x < 0 then return "negativus"
    if x ≡ 0 then return "nihil"
    return "positivus"
}

# Optional return: 空类型 when divisor is zero
fn divide(int a, int b) → int ∪ none {
    if b ≡ 0 then return null
    return a / b
}

# 否则如果 chain with 否则 则 返回 fallback
fn gradus(int puncta) → string {
    if puncta ≥ 90 then return "A"
    elif puncta ≥ 80 then return "B"
    elif puncta ≥ 70 then return "C"
    elif puncta ≥ 60 then return "D"
    else then return "F"
}

# Early return inside 遍历 取自 loop
fn inveni(list<int> res, int quaesitum) → int ∪ none {
    for from res const item {
        if item ≡ quaesitum then return item
    }
    return null
}

fn habet(map<string, int> map, string clavis) → bool {
    for ref map const k {
        if k ≡ clavis then return true
    }
    return false
}

main {
    # Sign classification
    print classis(-5)
    print classis(0)
    print classis(10)

    # Optional return on invalid divisor
    # 5
    print divide(10, 2)
    # 空类型
    print divide(10, 0)

    # Letter grades via 否则如果 chain
    print gradus(95)
    print gradus(85)
    print gradus(55)

    # Linear search with early 返回
    const _ numeri ← [1, 2, 3, 4, 5]
    print inveni(numeri, 3)
    print inveni(numeri, 9)
}

Expected output:

negativus
nihil
positivus
5
nihil
A
B
F
3
nihil

radix/corpus/si/ergo.fab (canonical · operator-group)#

Introduces a compact statement consequent.

# =============================================================================
# 则 — Introduces a compact statement consequent.
# =============================================================================
#
# What this teaches:
#   • Inline conditionals — `则` replaces a single-statement block body on
#     `如果` and `否则` branches
#   • `如果 <cond> 则 <stmt> 否则 则 <stmt>` forms a two-way one-liner
#     without braces
#
# Common mistakes:
#   • TODO: chaining multiple statements after `则` (it accepts only one
#     statement)
#
# See also: 如果, 当, 闭包, 返回, 静默
# =============================================================================

# One-liner conditionals with 则
#
# 如果 <condition> 则 <statement>                              -- single consequent
# 如果 <condition> 则 <statement> 否则 则 <statement>     -- if-else one-liner
#
# GRAMMAR:
#   ifStmt :← '如果' expr '则' stmt ('否则' '则' stmt)?
#
# EXPECTED OUTPUT:
#   Validation and grading lines for sample x, aetas, and puncta values.

main {
    # 则 replaces a one-statement block body
    const _ x ← 10

    if x ≻ 5 then print "x magnum est"

    # 否则 则 pairs else with a single consequent
    const _ aetas ← 25
    if aetas ≥ 18 then print "adultus"
    else then print "minor"

    # Two-way one-liner (85 < 90 → "非 A")
    const _ puncta ← 85
    if puncta ≥ 90 then print "A"
    else then print "non A"

    # 布尔 condition used directly
    const _ valet ← true
    if valet then print "Recte"
}

Expected output:

x magnum est
adultus
non A
Recte