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Other conventions are less common: Common Lisp and Macsyma/Maxima use Basic-like operators for numerical values, except for inequality, which is /= in Common Lisp and # in Macsyma/Maxima. Common Lisp has multiple other sets of equality and relational operators serving different purposes, including eq, eql, equal, equalp, and string=. [6]
The loop macro in ANSI Common Lisp is anaphoric in binding, where the it expression refers to the result of the test expression in a clause. [2] [3]Here is an example that sums the value of non-nil elements, where it refers to the values of elements that do not equal nil:
eq – given two expressions returns True if their values are equal; False if not if – given three expressions returns the value of the second if the value of the first is True, otherwise returns the value of the third lambda – given an argument list and an expression, returns them as a function
In early Lisp, the environment mapped each symbol to an association list, rather than directly to a value. [1] Standard keys for these lists included two keys used to store a data value, to be looked up when the symbol occurred as an argument (APVAL and APVAL1); and four keys used to store a function, to be looked up when the symbol occurred as an operator.
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation. [3] Originally specified in the late 1950s, it is the second-oldest high-level programming language still in common use, after Fortran.
(defvar *x*); Ensures that a variable *x* exists,; without giving it a value. The asterisks are part of; the name, by convention denoting a special (global) variable.; The symbol *x* is also hereby endowed with the property that; subsequent bindings of it are dynamic, rather than lexical.
MLisp was a contemporary (1968–1973) project to implement an M-expression-like frontend for Lisp. A few extra features like hygienic macros, pattern matching, and backtracking were incorporated. It eventually evolved into an abandoned LISP70 draft. M-LISP from 1989 was another attempt to blend M-expressions with Scheme. [7]