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Macaulay2Doc :: step

step -- step by single lines in the debugger

Synopsis

Description

One useful way to debug code suspected of being in error is to insert an explicit error message, such as error "debug me", and start stepping from there, as in the following demonstration.

i1 : load "Macaulay2Doc/demo2.m2"
i2 : code f

o2 = /home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:6:7-12:13: --source code:
     f = t -> (
          x := 1;
          error "debug me";
          y := t+1;
          z := 1/t;
          w := x+t;
          )
i3 : f 0
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6:(3):[1]: error: debug me
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6:(3):[1]: --entering debugger (type help to see debugger commands)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6-8:6: --source code:
     error "debug me";
ii4 : help

oo4 = --debugger activation depth control:
          errorDepth=3        -- activate at positions in user code (default)
          errorDepth=2        -- activate also at positions in packages
          errorDepth=1        -- activate also at positions in Core
          errorDepth=0        -- activate also at positions in the loader
      --debugging control:
          return              -- bypass current expression, return null, stop
          return x            -- bypass current expression, return x, stop
          step                -- step 1 line
          step n              -- step n lines
          step (-n)           -- trace n microsteps
          end (or eof char)   -- enter debugger one level up
          continue            -- leave the debugger, continuing execution
                              -- with current expression
          break               -- leave the debugger, returning to top level
      --debugging information:
          listLocalSymbols    -- display local symbols and their values
          listUserSymbols     -- display user symbols and their values
          current             -- the current expression; initially, the one
                              -- that produced an error
          code current        -- source code of current expression
          value current       -- execute current expression, obtain value
          disassemble current -- display microcode of current expression
          currentString       -- the string being evaluated by 'value', if
                              -- an error occurred within it
      -- emacs commands in *M2* buffer:
          RET                 -- on an file/position line, go to source
ii5 : return
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --stepping limit reached
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --entering debugger (type help to see debugger commands)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8-9:13: --source code:
     y := t+1;
ii6 : disassemble current

oo6 = (local-assign 2 0 (2-OP + (fetch 0 0) 1))
ii7 : step(-3)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --evaluating: (local-assign 2 0 (2-OP + (fetch 0 0) 1))
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:12:(3):[1]: --evaluating: (2-OP + (fetch 0 0) 1)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:11:(3):[1]: --evaluating: (fetch 0 0)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13:(3):[1]: --stepping limit reached
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13:(3):[1]: --entering debugger (type help to see debugger commands)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13-9:13: --source code:
     y := t+1;
ii8 : step
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8:(3):[1]: --stepping limit reached
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8:(3):[1]: --entering debugger (type help to see debugger commands)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8-10:13: --source code:
     z := 1/t;
ii9 : step
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:12:(3):[1]: error: division by zero
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:12:(3):[1]: --entering debugger (type help to see debugger commands)
/home2/dan/src/M2/M2/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:11-10:13: --source code:
     z := 1/t;
ii10 : t

oo10 = 0

See also

For the programmer

The object step is a keyword.