Module Twenty Three

Front 1

Thunk

Back 1

It is a zero argument function. We do not evaluate the expression now, we do it later when/if the function is called.

Front 2

Call-by-need

Back 2

The idea is to use mutation to remember the result from the first time we use the thunk so that we do not need to use the thunk again.

Front 3

Call-by-value

Back 3

Arguments are fully evaluated before the call is made.

Front 4

Stream

Back 4

An infinite sequence of values.

Front 5

Memoization

Back 5

An idiom related to lazy evaluation that does not actually use thunks is memoization.

If a function does nothave side-effects, then if we call it multiple times with the same argument(s), we do not actually have to dothe call more than once. Instead, we can look up what the answer was the first time we called the functionwith the argument(s).

Front 6

Macro definition

Back 6

A macro definition introduces some new syntax into the language. It describes how to transform the newsyntax into different syntax in the language itself.

Front 7

Macro expansion

Back 7

The process that replace the macro use with the appropriate syntax as defined by the macro definition.