[Haskell-beginners] Doubt in let expression

[Stephen Tetley]

Hello

There is no semantic implication of the difference.

http://haskell.org/onlinereport/syntax-iso.html

The Haskell syntax allows multiple declarations within a single let expression:

exp10 	 -> 	 ...
	| 	let decls in exp

where decls is a list of declarations, (braces and colons can be
replaced by layout):

decls 	 -> 	 { decl1  ; ... ; decln } 	

As a let ... in ... is an expression you can choose to write a list of
declarations as nested let instead as you did in the second version.

>From the original description of GHC intermediate form 'core' [1] page
3 shows that GHC chooses to desugar a let expression with a list of
decls into nested singular let expressions, though this might have
changed and also I might be misreading how GHC core distinguishes
recursive let declarations which do appear as lists.

Best wishes

Stephen


[1] An External Representation for the GHC Core Language (DRAFT for GHC5.02)
Andrew Tolmach and the GHC Team

GHC doesn't define Haskell of course...