expression_grammar.pegjs

{
	const globalScope = new Map();
    const getVar = (name) => {
    	if (!globalScope.has(name)) {
        	throw new Error("Unknown variable name");
        }
        return globalScope.get(name);
    };
    const filterEmpty = (arr) => arr.filter(v => typeof v === "number" || !v);
    
    const resolv = (x) => typeof x === "number" ? x : getVar(x);
    const sum = (e, t) => (x) => x + (e ? e(t) : t);
    const minus = (e, t) => (x) => { 
    	const diff = x - t;
        return e ? e(diff) : diff;
    }
    const mult = (e, t) => (x) => { 
    	const diff = x * t;
        return e ? e(diff) : diff;
    }
    const div = (e, t) => (x) => { 
    	const diff = x / t;
        return e ? e(diff) : diff;
    }
    const mod = (e, t) => (x) => { 
    	const diff = x % t;
        return e ? e(diff) : diff;
    }
}

S
	= i:Ident _ a:Assign { a.shift(); globalScope.set(i, a[0]); return a[0]; }
    / s:Op1 { return s; }

Assign
	= s:("=" _ Op1) { return filterEmpty(s); }

Op1
	= l:Term _ r:Exp { return  r ? r(resolv(l)) : resolv(l); }

_ = " "* { return; }

Exp
	= "+" _ t:Term _ e:Exp2 { return sum(e, resolv(t)); }
    / "-" _ t:Term _ e:Exp2 { return minus(e, resolv(t)); }
    / Exp2

Exp2
	= "/" _ t:Term _ e:Exp2 { return div(e, resolv(t)); }
    / "*" _ t:Term _ e:Exp2 { return mult(e, resolv(t)); }
    / "%" _ t:Term _ e:Exp2 { return mod(e, resolv(t)); }
    / "+" _ t:Term _ e:Exp2 { return sum(e, resolv(t)); }
    / "-" _ t:Term _ e:Exp2 { return minus(e, resolv(t)); }
    / Term
    / ""

Ident
	= ident:(Letter / "_" IdentChr) { return ident.join(''); }

IdentChr
	= "_" / Letter / Digit

Letter
	= [a-zA-Z]+

Digit
	= [0-9]+

Number
	= n:(Digit+ ("." Digit+)?) { return parseFloat(n.flat(Infinity).join('')); }

Term
 	= Number
    / Ident
    / "(" _ op:Op1 _ ")" { return op; }