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
  ┊ [int32]
il[3]> stloc i
  ┊ []
il[3]> LOOP: ldloc i
  ┊ [int32]
il[3]> ldc.i4.1
  ┊ [int32, int32] ◂ top
il[3]> add
  ┊ [int32]
il[3]> dup
  ┊ [int32, int32] ◂ top
il[3]> stloc i
  ┊ [int32]
il[3]> ldc.i4 10
  ┊ [int32, int32] ◂ top
il[3]> blt LOOP
  ┊ []
il[3]> ldloc i
  ┊ [int32]
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.

Methods persist the same way: .method int32 Twice(int32 n) { opens one, } closes it, and later cells call it with call int32 Twice(int32). Enter continues the block while its braces are open and sends it, line by line, once they balance; a pasted block waits for Enter the same way. See Methods and Editing blocks.

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: []
    add
    Expected: 2 stack values
    Stack before (bottom → top): []
    missing value: expected 2 more stack value(s); actual missing
il[4]> lcd.i4 1
  error: unknown opcode 'lcd.i4' (did you mean 'ldc.i4'?)

The model follows branches and checks the stack where paths meet. While editing, the status bar shows the stack before the instruction at the caret; F8 moves to the next diagnostic. .show lists the accepted body with the stack after each instruction. The runtime still checks the emitted IL when it compiles or runs.

Getting around

Tab completes opcodes, commands, types, and members, with a palette that shows each candidate’s stack effect. Up and Down choose palette rows; with the palette closed, they reach history from the first and last editor lines. History keeps a block as one entry and lasts between runs. .help prints the full command list, .ops lists opcodes, and Ctrl+Q leaves.