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elisp: Control Structures

 
 10 Control Structures
 *********************
 
 A Lisp program consists of a set of “expressions”, or “forms” (
 Forms).  We control the order of execution of these forms by enclosing
 them in “control structures”.  Control structures are special forms
 which control when, whether, or how many times to execute the forms they
 contain.
 
    The simplest order of execution is sequential execution: first form
 A, then form B, and so on.  This is what happens when you write several
 forms in succession in the body of a function, or at top level in a file
 of Lisp code—the forms are executed in the order written.  We call this
 “textual order”.  For example, if a function body consists of two forms
 A and B, evaluation of the function evaluates first A and then B.  The
 result of evaluating B becomes the value of the function.
 
    Explicit control structures make possible an order of execution other
 than sequential.
 
    Emacs Lisp provides several kinds of control structure, including
 other varieties of sequencing, conditionals, iteration, and (controlled)
 jumps—all discussed below.  The built-in control structures are special
 forms since their subforms are not necessarily evaluated or not
 evaluated sequentially.  You can use macros to define your own control
 structure constructs (Macros).
 

Menu

 
· Sequencing             Evaluation in textual order.
· Conditionals           ‘if’, ‘cond’, ‘when’, ‘unless’.
· Combining Conditions   ‘and’, ‘or’, ‘not’.
· Iteration              ‘while’ loops.
· Generators             Generic sequences and coroutines.
· Nonlocal Exits         Jumping out of a sequence.
 

Info Catalog elisp: Evaluation elisp: Top elisp: Variables