Conditional structures: Difference between revisions

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 =={{header|Ol}}==
-if-then, the simplest conditional primitive.
+if-then, the simplest conditional `if` primitive.
 <syntaxhighlight lang="scheme">
-(if (= (* 2 2) 4) (print "if-then: equal"))
+(if (= (* 2 2) 4)
-(if (= (* 2 2) 6) (print "if-then: non equal"))
+   (print "if-then: equal"))
+(if (= (* 2 2) 6)
+   (print "if-then: should not be printed"))
 ; ==> if-then: equal
 </syntaxhighlight>
-if-then-else, the full conditional 'if' primitive.
+if-then-else, the full conditional `if` primitive.
 <syntaxhighlight lang="scheme">
-(if (= (* 2 2) 4) (print "if-then-else: equal") (print "if-then-else: non equal"))
+(if (= (* 2 2) 4)
-(if (= (* 2 2) 6) (print "if-then-else: non equal") (print "if-then-else: i don't know"))
+   (print "if-then-else: equal")
+   (print "if-then-else: non equal"))
 ; ==> if-then-else: equal
-; ==> if-then-else: i don't know
+(if (= (* 2 2) 6)
+   (print "if-then-else: equal")
+   (print "if-then-else: non equal"))
+; ==> if-then-else: non equal
 </syntaxhighlight>
-unless, the opposite for 'if'.
+when and unless, the simplification of `if` without `begin`
 <syntaxhighlight lang="scheme">
-(unless (= (* 2 2) 4) (print "unless: non equal"))
+(when (= (* 2 2) 4)
-(unless (= (* 2 2) 6) (print "unless: i don't know"))
+   (print "when: ..just do something..")
-(unless (= (* 2 2) 4) (print "unless: non equal") (print "unless: equal"))
+   (print "when: equal"))
+; ==> when: ..just do something..
-(unless (= (* 2 2) 6) (print "unless: i don't know") (print "unless: non equal"))
-; ==> unless: i don't know
+; ==> when: equal
-; ==> unless: equal
+(unless (= (* 2 2) 6)
-; ==> unless: i don't know
+   (print "unless: ..just do something..")
+   (print "unless: not equal"))
+; ==> unless: ..just do something..
+; ==> unless: not equal
+</syntaxhighlight>
+if-then-else, extended conditional `if` primitive.
+<syntaxhighlight lang="scheme">
+(if (= (* 2 2) 4)
+   (print "if-then-else*: equal")
+else
+   (print "if-then-else*: ..just do something..")
+   (print "if-then-else*: non equal"))
+; ==> if-then-else*: equal
+(if (= (* 2 2) 4)
+then
+   (print "if-then-else*: ..just do something..")
+   (print "if-then-else*: equal")
+else
+   (print "if-then-else*: ..just do something..")
+   (print "if-then-else*: non equal"))
+; ==> if-then-else*: ..just do something..
+; ==> if-then-else*: equal
+(if (= (* 2 2) 4) ; same as `when`
+then
+   (print "if-then-else*: ..just do something..")
+   (print "if-then-else*: equal"))
+; ==> if-then-else*: ..just do something..
+; ==> if-then-else*: equal
 </syntaxhighlight>
@@ Line 5,266: / Line 5,304: @@
 <syntaxhighlight lang="scheme">
 (case (* 2 2)
-   (3
+   (3 ; exact number
       (print "case: 3"))
-   (4
+   (4 ; exact number
       (print "case: 4"))
-   ((5 6 7)
+   ((5 6 7) ; list of numbers
       (print "case: 5 or 6 or 7"))
    (else
       (print "case: i don't know")))
 ; ==> case: 4
-</syntaxhighlight>
+; extended case with usable else
-additionally, case can select vectors with variables filling
+(case (* 2 2)
-<syntaxhighlight lang="scheme">
+   (3 ; exact number
-(case (vector 'selector 1 2 3)
+      (print "case: 3"))
+   (else => (lambda (num)
+      (print "case: real value is " num))))
+; ==> case: real value is 4
+(case (* 2 2)
+   (3 ; exact number
+      (print "case: 3"))
+   (else is num
+      (print "case: real value is " num)))
+; ==> case: real value is 4
+; extended case with vectors
+(case ['selector 1 2 3]
    (['case1 x y]
       (print "case: case1 " x ", " y))
@@ Line 5,286: / Line 5,337: @@
    (else
       (print "case: i don't know")))
-; ==> tuple-case: selector 1, 2, 3
+; ==> case: selector 1, 2, 3
 </syntaxhighlight>