Chapter 6: reading errors

Three small programs, each with something wrong - two of them broken forms from chapter 6, Reading the Compiler's Guidance. The compiler has found one error so far, in greeting.ek9: the Problems tab lists it, and the editor underlines it. Read the code and find the underlined word. To play it in the IDE: Help > Lessons > Getting started…, or ek9 -ide -lesson fixing-errors.

The EK9 IDE as the lesson opens: the code to read and, in the Hovers panel, its error explained

Start from

The code the lesson starts from: copy it into a file of your own and follow the steps.

greeting.ek9

#!ek9
defines module errors.reading

  defines program

    Greeting()
      stdout <- Stdout()
      stdout.printn("hello")

check.ek9

#!ek9
defines module errors.reading

  defines program

    Check()
      -> score as Integer
      stdout <- Stdout()
      if score > 50
        stdout.println("pass")

weather.ek9

#!ek9
defines module errors.reading

  defines program

    Weather()
      stdout <- Stdout()
      temperature <- 14
      if temperature < 18
        stdout.println("Bring a jacket")

Step 1: Where an error shows

Click the error in the Problems tab. The editor opens that place.

The EK9 IDE once this is done: Click the error in the Problems tab

The editor marks the same place: a red circle in the margin beside line 8 and a red underline under printn. Rest the pointer on printn and a tooltip gives the code, E50060, and what the compiler thinks you meant.

The EK9 IDE once this is done: The editor marks the same place

Step 2: The quick fix

Click on printn and leave the pointer there a moment, then press Tab. The compiler offers the names that fit - print and println; Tab again moves to println and Enter takes it. (Clicking println under Quick Fixes in the Hovers panel does the same.) Then choose File > Save.

The EK9 IDE once this is done: Click on printn and leave the pointer there a moment, then press Tab

Step 3: The next errors

The compiler checks in stages and reports one stage's errors at a time. Names it cannot find come first; the later checks run once they are fixed. Now they have run: two more errors, in two files - a condition that is always true (E08086) and a bare number in a comparison (E11064).

The EK9 IDE once this is done: The compiler checks in stages and reports one stage's errors at a time

Choose Navigate > Next Error, or press F2. The editor jumps to the next error - in weather.ek9, the next file.

The EK9 IDE once this is done: Choose Navigate > Next Error, or press F2

Choose Next Error again. After the last error it starts again from the first, in check.ek9; Previous Error (Shift+F2) goes the other way.

The EK9 IDE once this is done: Choose Next Error again

Step 4: How much it says

Move the error-detail slider, at the right of the status bar, to E3.

The EK9 IDE once this is done: Move the error-detail slider, at the right of the status bar, to E3

At E3 the Build Output tab explains every error in full - what is wrong, why, and how to put it right. E0 is the bare minimum, E1 adds a picture of the place and E2, the usual, adds suggestions.

The EK9 IDE once this is done: At E3 the Build Output tab explains every error in full - what is wrong, why, and how to put it right

Move the slider back to E2.

The EK9 IDE once this is done: Move the slider back to E2

Step 5: The full explanation

Type /h E08086 in the input bar at the top and press Enter. The Help tab explains the error in full - the same text as ek9 -h E08086 in a terminal.

The EK9 IDE once this is done: Type /h E08086 in the input bar at the top and press Enter

The result

That is how to read the compiler: where an error is (the Problems tab, the margin, Next Error), a quick fix when the compiler can name the answer, as much detail as you want (E0 to E3), and /h with the error's code for everything it knows. The other two errors are still here - E08086 and E11064 - and each has a lesson that fixes it: ek9 -ide -lesson fix-E08086.

Where this lesson comes from

In the EK9 reference: Design note: errors, not warnings