haskell - How do `do` and `where` mix? -

from book have following code snippets

mutableupdateio :: int -> io (mv.mvector realworld int) mutableupdateio n =   mvec <- gm.new (n + 1)   go n mvec       go 0 v = return v     go n v = (mv.write v n 0) >> go (n - 1) v  mutableupdatest :: int -> v.vector int mutableupdatest n =   runst $     mvec <- gm.new (n + 1)     go n mvec       go 0 v = v.freeze v     go n v = (mv.write v n 0) >> go (n - 1) v 

like hindent indents them. want introduce braces , semicolons, whitespace isn't relevant more. because curious.

the second example suggests, where belongs whole runst $ ... expression, first example suggests, somehow part of go n mvec statement. reading in haskell report chapter 2.7 tried introduce braces , semicolons in first example like

mutableupdateio :: int -> io (mv.mvector realworld int) mutableupdateio n = {   mvec <- gm.new (n + 1);   go n mvec;   {     go 0 v = return v;     go n v = (mv.write v n 0) >> go (n - 1) v;   } ; } 

but parsing error. why that?

why layout hindent produces first example mutableupdateio valid haskell? shouldn't braces , semicolons introduced in above try?

the where blocks belong neither runst $ ... expression nor go n mvec statement; belong mutableupdateio n = ... declaration , mutableupdatest n = ... declaration. braces , semicolons should go this:

mutableupdateio :: int -> io (mv.mvector realworld int) mutableupdateio n = {   mvec <- gm.new (n + 1);   go n mvec;   } {     go 0 v = return v;     go n v = (mv.write v n 0) >> go (n - 1) v;   } 

the relevant sentence informal description in report in chapter 2.7 this:

a close brace inserted whenever syntactic category containing layout list ends; is, if illegal lexeme encountered @ point close brace legal, close brace inserted.

since where illegal lexeme inside expression, ends do block , close brace inserted there. explains why layout hindent produced legal.