Boolean

From Erights

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Latest revision as of 22:58, 10 January 2009

The Boolean type has exactly two members, false and true. All three of these objects print with those names.

? true
# value: true

? false
# value: false

? boolean
# value: Boolean

The universal scope contains boolean (no capital), false, and true.

Contents 1 Protocol 1.1 pick/2 1.2 not/0 1.3 or/1 1.4 and/1 1.5 xor/1 1.6 op__cmp/1

Protocol

pick/2

Signature: pick(t, f) :any

false.pick(t, f) returns f; true.pick(t, f) returns t.

? true.pick(1, 2)
# value: 1

? false.pick(3, 4)
# value: 4
 

not/0

Signature: not() :Boolean

Boolean negation.

? !true
# value: false

? !false
# value: true

or/1

Signature: or(other :Boolean) :Boolean

Boolean or. The argument is coerced to a boolean.

? false | false
# value: false

? false | true
# value: true

? false | def _{to __conformTo(==boolean) :any {return false}}
# value: false

? true | false
# value: true

? true | true
# value: true

? true | -1
# problem: the int -1 doesn't coerce to a boolean

? true | def _{to __conformTo(==boolean) :any {return true}}
# value: true

and/1

Signature: and(other :Boolean) :Boolean

Boolean and. The argument is coerced to a boolean.

? true & true
# value: true

? true & false
# value: false

? true & def _{to __conformTo(==boolean) :any {return true}}
# value: true

? false & true
# value: false

? false & false
# value: false

? false & -1
# problem: the int -1 doesn't coerce to a boolean

? false & def _{to __conformTo(==boolean) :any {return false}}
# value: false

XXX discuss ideal default wording of coercion failure errors

xor/1

Signature: xor(other :Boolean) :Boolean

Boolean exclusive or. The argument is coerced to a boolean.

? false ^ false
# value: false

? false ^ true
# value: true

? true ^ def _{to __conformTo(==boolean) :any {return true}}
# value: false

? true ^ false
# value: true

? true ^ true
# value: false

? false ^ -1
# problem: the int -1 doesn't coerce to a boolean

? false ^ def _{to __conformTo(==boolean) :any {return true}}
# value: true

op__cmp/1

Comparison with other Booleans. See Message op__cmp.

XXX write tests for this