Editing MUMPS (section)

=== Criticism ===
{{criticism section|date=February 2022}}

Some aspects of MUMPS syntax differ strongly from that of more modern languages, which can cause confusion, although those aspects vary between different versions of the language. On some versions, whitespace is not allowed within expressions, as it ends a statement: <code>2 + 3</code> is an error, and must be written <code>2+3</code>. All operators have the same precedence and are [[operator associativity|left-associative]] (<code>2+3*10</code> evaluates to 50). The operators for "less than or equal to" and "greater than or equal to" are <code>'></code> and <code>'<</code> (that is, the Boolean negation operator <code>'</code> plus a strict comparison operator in the opposite direction), although some versions allow the use of the more standard <code><=</code> and <code>>=</code> respectively. Periods (<code>.</code>) are used to indent the lines in a DO block, not whitespace. The ELSE command does not need a corresponding IF, as it operates by inspecting the value in the built-in system variable <code>$test</code>.

MUMPS [[scope (computer science)|scoping]] rules are more permissive than other modern languages. Declared local variables are scoped using the stack. A routine can normally see all declared locals of the routines below it on the call stack, and routines cannot prevent routines they call from modifying their declared locals, unless the caller manually creates a new stack level (<code>do</code>) and aliases each of the variables they wish to protect (<code>. new x,y</code>) before calling any child routines. By contrast, undeclared variables (variables created by using them, rather than declaration) are in scope for all routines running in the same process, and remain in scope until the program exits.

Because MUMPS database references differ from internal variable references only in the caret prefix, it is dangerously easy to unintentionally edit the database, or even to delete a database "table".{{r|Richmond_1984_Thesis}}