Page:Scheme - An interpreter for extended lambda calculus.djvu/12

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Sussman and Steele December 22, 1975 11 SCHEME Programming Examples

potential need for backtracking enters, for segments of various lengths may have to be tried. After MATCH* matches a segment, it calls MATCH1 to continue the match, giving it a failure continuation which will back up and try to match a longer segment if possible. A failure can occur if a constant fails to match, or if one or the other of pattern and expression runs out before the other one does.