General Computer Science 320201 GenCS I & II Lecture ... - Kwarc

Compiling µML Expressions (Continued)
fun compileE (e:exp, env:env, tail:code) : code =
case e of
Con i => [con i] @ tail
| Id i => [arg((lookupA(i,env)))] @ tail
| Add(e1,e2) => compileEs([e1,e2], env) @ [add] @ tail
| Sub(e1,e2) => compileEs([e1,e2], env) @ [sub] @ tail
| Mul(e1,e2) => compileEs([e1,e2], env) @ [mul] @ tail
| Leq(e1,e2) => compileEs([e1,e2], env) @ [leq] @ tail
| If(e1,e2,e3) => let
val c1 = compileE(e1,env,nil)
val c2 = compileE(e2,env,tail)
val c3 = compileE(e3,env,tail)
in if null tail
then c1 @ [cjp (4+wlen c2)] @ c2
@ [jp (2+wlen c3)] @ c3
else c1 @ [cjp (2+wlen c2)] @ c2 @ c3
end
| App(i, es) => compileEs(es,env) @ [call (lookupP(i,env))] @ tail
and (* mutual recursion with compileE *)
fun compileEs (es : exp list, env:env) : code =
foldl (fn (e,c) => compileE(e, env, nil) @ c) nil es
c○: Michael Kohlhase 321
Now we turn to the declarations compiler. This is considerably more complex than the one for
SW we had before due to the presence of formal arguments in the function declarations. We
first define a function that inserts function arguments into an environment. Then we use that
in the expression compiler to insert the function name and the list of formal arugments into the
environment for later reference. In this environment env’’ we compile the body of the function
(which may contain the formal arugments). Observe the use of the tail arugment for compileE to
pass the return command. Note that we compile the rest of the declarations in the environment
env’ that contains the function name, but not the function arguments.
Compiling µML Expressions (Continued)
fun insertArgs’ (i, (env, ai)) = (insert(i,Arg ai,env), ai+1)
fun insertArgs (is, env) = (foldl insertArgs’ (env,1) is)
fun compileD (ds: declaration list, env:env, ca:ca) : code*env =
case ds of
nil => (nil,env)
| (i,is,e)::dr =>
let
val env’ = insert(i, Proc(ca+1), env)
val env’’ = insertArgs(is, env’)
val ce = compileE(e, env’’, [return])
val cd = [proc (length is, 3+wlen ce)] @ ce
(* 3+wlen ce = wlen cd *)
val (cdr,env’’) = compileD(dr, env’, ca + wlen cd)
in
(cd @ cdr, env’’)
end
c○: Michael Kohlhase 322
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