Function Repository Resource:

CheckReturn

Evaluate an expression that returns the result unless messages were generated, in which case it immediately returns a Failure expression

Contributed by: Carl Woll

ResourceFunction["CheckReturn"][expr]

returns the evaluation of expr unless a message was generated, in which case it immediately returns $Failed.

ResourceFunction["CheckReturn"][expr,failexpr]

evaluates and returns failexpr when a message is generated.

ResourceFunction["CheckReturn"][expr,failexpr,{s₁::t₁,s₂::t₂,…}]

checks only for the specified messages.

ResourceFunction["CheckReturn"][expr,failexpr,"name"]

checks only for messages in the named message group.

ResourceFunction["CheckReturn"][expr,failexpr,messages,listen]

checks for the messages listen even if they have been quieted during the evaluation of expr.

Details

ResourceFunction["CheckReturn"] has the attribute HoldAll

In ResourceFunction["CheckReturn"][expr,failexpr,"name"], possible named message groups are given by $MessageGroups.

Explicit message names of the form s::t can be mixed with named message groups.

ResourceFunction["CheckReturn"][expr,failexpr,m] does not test for messages that have been switched off using Off, or by uses of Quiet that occur inside it.

Use ResourceFunction["CheckReturn"][expr,failexpr,m,listen] to test for messages that have been quieted due to uses of Quiet that occur inside expr.

Examples

Basic Examples (3)

CheckReturn returns the failure expression immediately, without finishing evaluation:

In[1]:=

Out[1]=

Check only for specific messages:

In[2]:=

Out[2]=

In[3]:=

Out[3]=

For a single argument, failures give $Failed:

In[4]:=

Out[4]=

Scope (3)

CheckReturn does not detect messages suppressed with an inner Quiet:

In[5]:=

Out[5]=

However, the operation of CheckReturn is not affected by being inside Quiet:

In[6]:=

Out[6]=

Use the fourth argument to detect messages that have been suppressed with an inner Quiet:

In[7]:=

Out[7]=

Properties and Relations (2)

CheckReturn is similar to FailOnMessage, except that the third argument is a list of messages that should trigger the message:

In[8]:=

Out[8]=

The third argument of the resource function FailOnMessage specifies a message that should be ignored:

In[9]:=

Out[9]=

To achieve the same behavior, the fourth argument is needed:

In[10]:=

Out[10]=

When a Quiet is used to suppress messages, CheckReturn will respect the Quiet:

In[11]:=

Out[11]=

Check behaves similarly:

In[12]:=

Out[12]=

In the following, CheckReturn only returns after the second, unquieted division by zero occurs:

In[13]:=

Out[13]=

It is not possible to achieve this behavior with the resource function FailOnMessage, as the return occurs during the quieted division by zero (since the Print never occurs):

In[14]:=