then

Introduces a compact statement consequent.

Aliases: ergo, therefore

Syntax: <head> then <statement>

Category#

control-flow

Related#

• if
• return
• lambda
• ergo

Examples#

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

Compact consequent after if/dum heads via then, with ∴ reserved for closure bodies.

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

# operatores/control — then therefore consequent
#
# GRAMMAR:
#   consequentStmt :← ('if' | 'elif' | 'else' | 'while') expr 'then' stmt
#
# EXPECTED OUTPUT:
#   0, 100, 42
#
# BACKEND:
#   Cross-ref if/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.

# =============================================================================
# then — Introduces a compact statement consequent.
# =============================================================================
#
# What this teaches:
#   • Guard clauses — `if <cond> then return <expr>` provides a compact
#     one-liner for early returns
#   • `elif` and `else` also accept `then` for chained guard expressions
#   • Demonstrates guard-return patterns, optional returns, and linear search
#
# Common mistakes:
#   • TODO: using `then` with a block instead of a single statement
#
# See also: if, while, lambda, return, pass
# =============================================================================

# Si with then return syntax
#
# if <conditio> then return <expressio>     -- guard return
# elif <conditio> then return <expressio>    -- else-if guard
# else then return <expressio>             -- else return
#
# GRAMMAR:
#   guardReturn :← ('if' | 'elif' | 'else') expr 'then' 'return' 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: none when divisor is zero
fn divide(int a, int b) → int ∪ none {
    if b ≡ 0 then return null
    return a / b
}

# elif chain with else then return 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 for from 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)
    # none
    print divide(10, 0)

    # Letter grades via elif chain
    print gradus(95)
    print gradus(85)
    print gradus(55)

    # Linear search with early return
    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.

# =============================================================================
# then — Introduces a compact statement consequent.
# =============================================================================
#
# What this teaches:
#   • Inline conditionals — `then` replaces a single-statement block body on
#     `if` and `else` branches
#   • `if <cond> then <stmt> else then <stmt>` forms a two-way one-liner
#     without braces
#
# Common mistakes:
#   • TODO: chaining multiple statements after `then` (it accepts only one
#     statement)
#
# See also: if, while, lambda, return, pass
# =============================================================================

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

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

    if x ≻ 5 then print "x magnum est"

    # else then 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 → "not A")
    const _ puncta ← 85
    if puncta ≥ 90 then print "A"
    else then print "non A"

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

Expected output:

x magnum est
adultus
non A
Recte