Quick start

Start ilrepl and type an instruction. The line under it is the simulated evaluation stack, bottom to top.

il[1]> ldc.i4 6
  ┊ [int32]
il[1]> ldc.i4 7
  ┊ [int32, int32] ◂ top
il[1]> mul
  ┊ [int32]
il[1]> ret
  = 42 : int32

ret, or an empty line, compiles everything you typed since the last run into a method, runs it, and prints whatever single value was left on the stack. An empty stack means the cell was void.

Calls

Member references use ILAsm syntax, with two conveniences: the return type and the [assembly] prefix are optional, and short type names resolve through the common System namespaces.

il[2]> ldstr "hello"
  ┊ [string]
il[2]> callvirt instance int32 String::get_Length()
  ┊ [int32]
il[2]> ret
  = 5 : int32

When a name is ambiguous the error lists the overloads so you can pick one.

Locals and loops

Locals are declared with .locals and persist across cells. Their values do not; each run starts fresh.

il[3]> .locals init (int32 i)
  locals: 0:int32 i
il[3]> ldc.i4.0
il[3]> stloc i
il[3]> LOOP: ldloc i
il[3]> ldc.i4.1
il[3]> add
il[3]> dup
il[3]> stloc i
il[3]> ldc.i4 10
il[3]> blt LOOP
il[3]> ldloc i
il[3]> ret
  = 10 : int32

A label is a name followed by a colon, on its own line or before an instruction. A branch to a label that has not been defined yet is fine; the cell will not run until it is.

Mistakes

The stack model catches the common ones before the runtime sees them.

il[4]> add
  error: stack underflow: 'add' pops 2 values but the stack has 0: []
il[4]> lcd.i4 1
  error: unknown opcode 'lcd.i4' (did you mean 'ldc.i4'?)

Anything the model cannot catch, such as a stack that differs between two branches into the same label, is reported when the JIT rejects the cell. .show lists the cell with the stack after each instruction, which is usually enough to find it.

Getting around

Tab completes opcodes and commands, with a palette that shows each candidate’s stack transition. Up and Down walk history. .help prints the full command list, .ops lists opcodes, and Ctrl+Q leaves.