8.1 Recursive definitions of values

(Introduced in Objective Caml 1.00)

As mentioned in section ‍7.7.2, the let rec binding construct, in addition to the definition of recursive functions, also supports a certain class of recursive definitions of non-functional values, such as

which binds name₁ to the cyclic list 1::2::1::2::…, and name₂ to the cyclic list 2::1::2::1::…Informally, the class of accepted definitions consists of those definitions where the defined names occur only inside function bodies or as argument to a data constructor.

More precisely, consider the expression:

It will be accepted if each one of expr₁ …  expr_n is statically constructive with respect to name₁ …  name_n, is not immediately linked to any of name₁ …  name_n, and is not an array constructor whose arguments have abstract type.

An expression e is said to be statically constructive with respect to the variables name₁ …  name_n if at least one of the following conditions is true:

• e has no free occurrence of any of name₁ …  name_n
• e is a variable
• e has the form fun … -> …
• e has the form function … -> …
• e has the form lazy ( … )
• e has one of the following forms, where each one of expr₁ …  expr_m is statically constructive with respect to name₁ …  name_n, and expr₀ is statically constructive with respect to name₁ …  name_n,  xname₁ …  xname_m:
  • let [rec] xname₁ =  expr₁ and … and  xname_m =  expr_m in  expr₀
  • let module … in expr₁
  • constr ( expr₁, … ,  expr_m)
  • `tag-name ( expr₁, … ,  expr_m)
  • [| expr₁; … ;  expr_m |]
  • { field₁ =  expr₁; … ;  field_m =  expr_m }
  • { expr₁ with  field₂ =  expr₂; … ;  field_m =  expr_m } where expr₁ is not immediately linked to name₁ …  name_n
  • ( expr₁, … ,  expr_m )
  • expr₁; … ;  expr_m

An expression e is said to be immediately linked to the variable name in the following cases:

• e is name
• e has the form expr₁; … ;  expr_m where expr_m is immediately linked to name
• e has the form let [rec] xname₁ =  expr₁ and … and  xname_m =  expr_m in  expr₀ where expr₀ is immediately linked to name or to one of the xname_i such that expr_i is immediately linked to name.