Been messing round with the following Happy grammar :-

%token

'let' { TokenIdent "let" }

'in' { TokenIdent "in" }

ident { TokenIdent $$ }

int { TokenInt $$ }

'=' { TokenEq }

'+' { TokenPlus }

'-' { TokenMinus }

'*' { TokenTimes }

'/' { TokenDiv }

'(' { TokenOB }

')' { TokenCB }

Exp : 'let' Var '=' Exp 'in' Exp { Let $2 $4 $6 }

| Exp1 { Exp1 $1 }

Exp1 : Exp1 '+' Term { Plus $1 $3 }

| Exp1 '-' Term { Minus $1 $3 }

| Term { Term $1 }

Term : Term '*' Factor { Times $1 $3 }

| Term '/' Factor { Div $1 $3 }

| Factor { Factor $1 }

Factor :: { Factor }

: int { Int $1 }

| ident { Var $1 }

| '(' Exp ')' { Brack $2 }

Var :: { Factor }

: ident { Var $1 }

| 'let' { Var "let" }

Here 'Var' should be able to represent a 'let' identifier, as well as a keyword. Happy accepts the grammar but it does not parser the expected 'let let = x in let'.

I have attached the full Happy grammar.

I don't think this is an LR thing, but could be wrong.

Many thanks in advance,

Aaron