CIDER Debug

Instrument one or more expressions or function definitions to use the Cider step debug tool, showing intermittent values from evaluating each form in turn.

Debug functions

, d b with the cursor over a function definition calls the cider-debug-defn-breakpoint command, setting breakpoints throughout the function definition.

Evaluate a call to the function, e.g. , e f, to start the cider debug tool.

A debug menu appears above the expression, press n to step through each expression and see the inline result.

Cider debug key bindings

Evil key conflict - switch to Emacs Edit mode for full menu

C-z after starting cider-debug to use c e i p s menu keys as otherwise they call the Evil normal state commands. C-z to switch back to Evil normal state once debug is complete.

#dbg tag to debug a form

#dbg tag before a form is the same as calling , d b to create breakpoints throughout an expression or function definition

Skip over lazy functions

o (out) will jump out of evaluating an expression.

Use out to jump over evaluating code that has functions generating lazy infinite sequences, such as range or cycle. Cider debug will then evaluate those functions in their outer expression where it should be safe to do so.

Debug expressions

Debug an expression in the same way as a function definition.

Debug break point scope

Using , d b on an expression that calls a function will not add break points to the function being called.

Remove debug instrumentation

Evaluate the function definition or expression to remove the debug instrumentation and all breakpoints.

Conditional break points

:break/when metadata on a #dbg directive defines a condition when a breakpoint is triggered, allowing the evaluation to iterate until a desirable point is reached.

Setting a condition is especially useful when there are many iterations required before reaching a point of issue, for example iterating through a large data set.

A #break can be added on any Clojure form. In this example the evaluation will break on each iteration of the sequence, showing the local value of the index.

(dotimes [index 10]
  #break index)

Add a break condition within the expression to be evaluated and the evaluation will iterate until the condition is met and then break

n to continue to the next break point will complete the evaluation as the break condition is no longer met

(dotimes [index 10]
  #dbg ^{:break/when (= index  7)}
  index)

The evaluation will break each time a condition is met, so a break will occur multiple times when the value of index is odd

(dotimes [index 10]
  #dbg ^{:break/when (odd? index)}
   index)

References

• Conditional Breakpoints in the Cider debugger

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Last update: July 1, 2023