MoggiThe REPL
The REPL is the fastest way to try a piece of Moggi: type an expression, get its value; ask for a type; load a file and poke at it. Nothing is compiled to an artifact and nothing is left on disk.
moggi repl
Moggi REPL (php). Type :help for commands, :quit to exit.
> 1 + 2
3
> "Hello, " <> "world!"
Hello, world!
> map (\x -> x * 2) [1, 2, 3]
[2,4,6]
> add 1
<function>
What you can type
- Expressions are evaluated and printed:
1 + 2,show (Circle 3.0),map (+ 1) [1, 2, 3]. - Declarations persist for the rest of the session:
double x = x * 2andtwice :: Int -> Intare as usable as a binding you type inside an expression.:browselists what you have defined. - Imports too:
import Data.List as L, thenL.unzip [(1,"a")]. A name that is not in scope is a normal compile error here, not a special REPL case. - Partial application shows its value:
add 1is a function, and:type add 1saysInt -> Int.
Commands
Every command starts with :. :help prints this list.
| Command | What it does |
|---|---|
:type expr, :t |
the type of an expression or binding |
:kind Type, :k |
the kind of a type (or of an expression’s type) |
:info Name, :i |
declaration information for a name |
:load file, :l |
load a module, so its definitions are in scope |
:reload, :r |
reload the loaded module after editing it |
:browse |
list the bindings defined in this session |
:show imports |
show the active imports |
:module [Name] |
show or set the interactive module name |
:history |
command history |
:clear |
reset the interactive state |
:backend php\|jvm\|dotnet |
switch the evaluation backend |
:quit, :q |
exit |
> :type putStrLn
putStrLn :: String -> IO ()
> :kind Maybe
Maybe :: Type -> Type
> :load Demo/Shapes.mog
> area (Circle 2.0)
12.566370614359172
:backend is worth noticing once: the REPL evaluates on the backend you select,
so :backend jvm is how you check that a program behaves the same off PHP —
including the host calls in a foreign jvm declaration.
Looking inside the compiler
The same stages the compiler runs are available for a fragment, or for the whole interactive module:
| Command | Shows |
|---|---|
:ast [expr\|decl] |
the parsed tree |
:ir [expr\|decl] |
backend-neutral IR |
:ir-opt [expr\|decl] |
IR after optimization |
:emit [expr\|decl] |
the generated host code for the fragment |
:emit-opt [expr\|decl] |
the same, optimized |
:dump ast\|typed-ast\|ir\|ir-opt\|emit\|emit-opt |
that stage of the whole interactive module |
For a file rather than a session, one flag each does the same and prints to stdout:
moggi compile hello.mog --tokens # the token stream
moggi compile hello.mog --ast # the parsed tree
moggi compile hello.mog --typed-ast # after type checking and elaboration
moggi compile hello.mog --ir # backend-neutral IR
moggi compile hello.mog --opt-ir # after optimization
pipeline.md explains what each stage produces and where it lives, and optimizations.md documents the passes themselves.
Next
stdlib.md — find your way around the standard library.