Rewrites on Let Expressions

Externals relating to Let expressions.

e ==> (let v = e in v), name of v is provided

(let v = ev in e) x ==> let v = ev in e x

f (let v = ev in e) ==> let v = ev in f e

let v = (let w = ew in ev) in e ==> let w = ew in let v = ev in e

( v1 -> let v2 = e1 in e2) ==> let v2 = e1 in ( v1 -> e2) Fails if v1 occurs in e1. If v1 = v2 then v1 will be alpha-renamed.

case (let bnds in e) of wild alts ==> let bnds in (case e of wild alts) Fails if any variables bound in bnds occurs in alts.

cast (let bnds in e) co ==> let bnds in cast e co

Float a Let through an expression, whatever the context.

ProgCons (NonRec v (Let (NonRec w ew) ev)) p ==> ProgCons (NonRec w ew) (ProgCons (NonRec v ev) p)

Remove an unused non-recursive let binding. let v = E1 in E2 ==> E2, if v is not free in E2

Remove all unused recursive let bindings in the current group.

let v = ev in e ==> case ev of v -> e

Unfloat a Let if possible.

let v = ev in f a ==> (let v = ev in f) (let v = ev in a)

let v = ev in case s of p -> e ==> case (let v = ev in s) of p -> let v = ev in e, if v does not shadow a pattern binder in p

let v = ev in x -> e ==> x -> let v = ev in e if v does not shadow x

Re-order a sequence of nested non-recursive let bindings. The argument list should contain the let-bound variables, in the desired order.