diff --git a/example.gby b/example.gby
index a040d15..73067e6 100644
--- a/example.gby
+++ b/example.gby
@@ -1,3 +1,5 @@
 u8 x;
+u8 y;
 
 x <- 1;
+y <- -x;
diff --git a/lib/asm.ts b/lib/asm.ts
index 5ba4fe7..998afbc 100644
--- a/lib/asm.ts
+++ b/lib/asm.ts
@@ -129,14 +129,14 @@ export const convertASM_SSA_Unary = (state: ASMState, ssa: SSAUnary): void => {
     }
 
     switch (ssa.op) {
-        case '-':
+        case 'arith_negate':
             state.insns.push(
                 `CPL`,
                 `INC A`,
             )
             break
 
-        case '~':
+        case 'bit_negate':
             state.insns.push(
                 `CPL`
             )
diff --git a/lib/ast.d.ts b/lib/ast.d.ts
index e8e6030..98887ab 100644
--- a/lib/ast.d.ts
+++ b/lib/ast.d.ts
@@ -30,7 +30,15 @@ type AStmt<Ty, Args> = {
 }
 
 // Expressions
-export type Expr = number
+export type Expr = UnaryExpr | BasicExpr
+
+type UnaryExpr = {
+    type: "unary",
+    op: string,
+    arg: Expr,
+}
+
+type BasicExpr = number | string
 
 // Attributes
 export type Attr = {
diff --git a/lib/ir.ts b/lib/ir.ts
index 4aa7f82..e1ffdab 100644
--- a/lib/ir.ts
+++ b/lib/ir.ts
@@ -1,6 +1,5 @@
 import type { AssignStmt, Expr, Stmt } from "./ast"
 
-// dest <- op(x, y)
 type Operand = string | number
 
 type ASSA<Data> = { dest: string, source: Operand } & Data
@@ -44,9 +43,21 @@ export const convertAssignStmt = (state: IRState, stmt: AssignStmt): Array<SSA>
     return expr_stmts
 }
 
-export const convertExpr = (state: IRState, expr: Expr): [string, Array<SSA>] => {
+export const convertExpr = (state: IRState, expr: Expr): [string | number, Array<SSA>] => {
+    if (typeof expr === "number" || typeof expr === "string") {
+        return [expr, []]
+    }
+
+    const [source, expr_stmts] = convertExpr(state, expr.arg)
+
     const name = `temp${state.nextID++}`
-    return [name, [{ dest: name, source: expr }]]
+    expr_stmts.push({
+        dest: name,
+        source,
+        op: expr.op,
+    })
+
+    return [name, expr_stmts]
 }
 
 export const prettyPrintIR = (ssa: SSA): string => {
diff --git a/lib/parser.pegjs b/lib/parser.pegjs
index b929f71..1d8a373 100644
--- a/lib/parser.pegjs
+++ b/lib/parser.pegjs
@@ -3,6 +3,8 @@
     const attr = (name, args) => ({ name, args })
     const stmt = (stmt_type, args) => ({ type: "stmt", stmt_type, args })
     const decl = (decl_type, name, attrs, args) => ({ type: "decl", decl_type, name, attrs: attrs || [], args })
+    const uexpr = (op, arg) => ({ type: "unary", op, arg })
+    const bexpr = (op, arg1, arg2) => ({ type: "binary", op, arg1, arg2 })
 }
 
 Program = WS @(Decl / Stmt)* WS
@@ -16,8 +18,13 @@ Stmt = @AssignStmt SEMI
 AssignStmt = name:Ident ASSIGN expr:Expr { return stmt("assign", { name, expr }) }
 
 // Expressions
-Expr = BaseExpr
-BaseExpr = Number
+Expr = UnaryExpr
+
+UnaryExpr = op:UnaryOp? e:BaseExpr { return op ? uexpr(op, e) : e }
+UnaryOp = TILDE { return "bit_negate" }
+    / MINUS { return "arith_negate" }
+
+BaseExpr = Ident / Number / LPAREN @Expr RPAREN
 
 // Attributes
 Attrs = LATTR @AttrList RATTR
@@ -44,6 +51,8 @@ U8 = @'u8' WS
 U16 = @'u16' WS
 
 // Terminal symbols
+TILDE = '~' WS
+MINUS = '-' WS
 SEMI = ';' WS
 ASSIGN = '<-' WS
 LPAREN = '(' WS