1if ( ..a x pred: ( ..a x quot: ( ..a x -- ..b ? ) -- ..b x ? ) true: ( ..b x -- ..c ) false: ( ..b x -- ..c ) -- ..c )
Factor handbook » The language » Combinators » Conditional combinators

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Next:	2if ( ..a x y pred: ( ..a x y -- ..b x y ? ) true: ( ..b x y -- ..c ) false: ( ..b x y -- ..c ) -- ..c )

Vocabulary
kernel

Inputs

x	an object
pred	a quotation
true	a quotation
false	a quotation

Outputs
None

Word description
A variant of if that takes a pred quotation. Calls 1check on the pred quotation to return a boolean and preserves x for the true or false branches, one of which is called.

Examples
Collatz Conjecture calculation:

USING: kernel math prettyprint ; 6 [ even? ] [ 2 / ] [ 3 * 1 + ] 1if .
3

See also
1when, 1unless, 2if, 2when, 2unless, 3if, 3when, 3unless

Definition

IN: kernel

: 1if
    ( ..a x pred: ( ..a x quot: ( ..a x -- ..b ? ) -- ..b x ? ) true: ( ..b x -- ..c ) false: ( ..b x -- ..c ) -- ..c )
    [ 1check ] 2dip if ; inline