Editing Reserved word (section)

==Distinction==
When using an Interactive Development Environment (IDE) to develop a program, the IDE will generally highlight reserved words by displaying them in a different colour. In some IDEs, comments may also be highlighted (in yet another colour).  This makes it easy for a programmer to notice unexpected use of a reserved word and/or failure to terminate a comment correctly.

There may be reserved words which are not keywords. For example, in Java, <code>true</code>  and <code>false</code> are reserved words used as Boolean (logical) literals.  As another example, in Pascal, <code>div</code> and <code>mod</code> are reserved words used as operators (integer division and remainder).

There may also be reserved words which have no defined meaning.  For example, in Java, <code>goto</code> and <code>const</code> are listed as reserved words, but are not otherwise mentioned in the Java syntax rules.

A keyword such as '''if''' or '''while''' is used during [[parser|syntax analysis]] to determine what sort of statement is being considered. Such analysis is much simpler if keywords are either reserved or stropped. Consider the complexity of using contextual analysis in Fortran 77 to distinguish:
  IF (B) l1,l2      ! two-way branch, where B is a boolean/logical expression  
  IF (N) l1,l2,l3   ! three-way branch, where N is a numeric expression
  IF (B) THEN       ! start conditional block
  IF (B) THEN = 3.1 ! conditional assignment to variable THEN
  IF (B) X = 10     ! single conditional statement
  IF (B) GOTO l4    ! conditional jump
  IF (N) = 2        ! assignment to a subscripted variable named IF
PL/I can also allow some apparently confusing constructions:
  IF IF = THEN THEN ...    /* (the second <code>IF</code> and the first <code>THEN</code> are variables */