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Compilers 101: An introduction to programming l...

Compilers 101: An introduction to programming languages and parsing

I gave this talk at Coderfaire, August 17, 2013. As usual, the slides do not make a ton of sense without the words. Sorry!

However they contain a complete recursive-descent parser for a toy grammar, in JS. I’ve never given a talk with this much code before. The slides reveal this code line by line, and that worked out very nicely.

More resources for this talk: http://gist.io/6256943

Jason Orendorff

August 17, 2013
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  1. 17 August 2013 Compilers 101 An introduction to programming languages

    and parsing WARNING CONTAINS CODE 0 0 0 1 1 Tuesday, September 3, 13
  2. A compiler is a program that translates code from one

    language to another. Tuesday, September 3, 13
  3. A compiler is a program that translates code from one

    language to another. ✤ to machine code (like FORTRAN, C, Go) Tuesday, September 3, 13
  4. A compiler is a program that translates code from one

    language to another. ✤ to machine code (like FORTRAN, C, Go) ✤ to bytecode (like Java, Python) Tuesday, September 3, 13
  5. A compiler is a program that translates code from one

    language to another. ✤ to machine code (like FORTRAN, C, Go) ✤ to bytecode (like Java, Python) ✤ to another high-level language (cfront, LESS & Sass, CoffeeScript, Traceur, emscripten) Tuesday, September 3, 13
  6. Language is a different kind of data. It’s not line-based.

    It’s not record-based. Tuesday, September 3, 13
  7. Language is a different kind of data. It’s not line-based.

    It’s not record-based. And you can’t fake understanding. Tuesday, September 3, 13
  8. Language is a different kind of data. It’s not line-based.

    It’s not record-based. And you can’t fake understanding. Language has structure. Tuesday, September 3, 13
  9. when flag clicked forever point towards mouse-pointer if move 3

    * speed steps not touching mouse-pointer ? then Tuesday, September 3, 13
  10. when flag clicked forever point towards mouse-pointer if move 3

    * speed steps not touching mouse-pointer ? then Tuesday, September 3, 13
  11. front end (parsing, analysis) back end (code generation) sleep(2*x) pushq

    %rbp movq %rsp, %rbp addl %edi, %edi callq _sleep Inside a compiler Tuesday, September 3, 13
  12. front end (parsing, analysis) back end (code generation) sleep(2*x) call

    sleep * 2 x pushq %rbp movq %rsp, %rbp addl %edi, %edi callq _sleep Inside a compiler Tuesday, September 3, 13
  13. Inside a front end tokenizer parser AST builder 12*x *

    12 x ['12', '*', 'x'] Tuesday, September 3, 13
  14. Inside a front end tokenizer parser AST builder 12*x *

    12 x ['12', '*', 'x'] Tuesday, September 3, 13
  15. Inside a front end tokenizer parser AST builder 12*x *

    12 x ['12', '*', 'x'] out.number('12') Tuesday, September 3, 13
  16. Inside a front end tokenizer parser AST builder 12*x *

    12 x ['12', '*', 'x'] out.number('12') out.name('x') Tuesday, September 3, 13
  17. Inside a front end tokenizer parser AST builder 12*x *

    12 x ['12', '*', 'x'] out.number('12') out.name('x') out.mul( , ) Tuesday, September 3, 13
  18. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement Tuesday, September 3, 13
  19. PrimaryExpr : Number Name ( Expr ) MulExpr : PrimaryExpr

    ( * PrimaryExpr | / PrimaryExpr )* Expr : MulExpr ( + MulExpr | - MulExpr )* Tuesday, September 3, 13
  20. PrimaryExpr : Number Name ( Expr ) MulExpr : PrimaryExpr

    ( * PrimaryExpr | / PrimaryExpr )* Expr : MulExpr ( + MulExpr | - MulExpr )* out.number("3") Tuesday, September 3, 13
  21. PrimaryExpr : Number Name ( Expr ) MulExpr : PrimaryExpr

    ( * PrimaryExpr | / PrimaryExpr )* Expr : MulExpr ( + MulExpr | - MulExpr )* out.number("3") out.name("pi") Tuesday, September 3, 13
  22. PrimaryExpr : Number Name ( Expr ) MulExpr : PrimaryExpr

    ( * PrimaryExpr | / PrimaryExpr )* Expr : MulExpr ( + MulExpr | - MulExpr )* out.number("3") out.name("pi") out.mul(lhs, rhs) Tuesday, September 3, 13
  23. PrimaryExpr : Number Name ( Expr ) MulExpr : PrimaryExpr

    ( * PrimaryExpr | / PrimaryExpr )* Expr : MulExpr ( + MulExpr | - MulExpr )* out.number("3") out.name("pi") out.mul(lhs, rhs) out.add(lhs, rhs) Tuesday, September 3, 13
  24. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  25. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  26. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  27. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  28. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  29. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  30. function parse(code, out) { var tokens = tokenize(code); var position

    = 0; function peek() { return tokens[position]; } function consume(token) { assert.strictEqual(token, tokens[position]); position++; } Calculator parser - page 1 of 5 Tuesday, September 3, 13
  31. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  32. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  33. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  34. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  35. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  36. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  37. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  38. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  39. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  40. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  41. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  42. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  43. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  44. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  45. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  46. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  47. function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) {

    consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Calculator parser - page 2 of 5 PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  48. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  49. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  50. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  51. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  52. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  53. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  54. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  55. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  56. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  57. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  58. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  59. function parseMulExpr() { var expr = parsePrimaryExpr(); var t =

    peek(); while (t === "*" || t === "/") { consume(t); var rhs = parsePrimaryExpr(); if (t === "*") expr = out.mul(expr, rhs); else expr = out.div(expr, rhs); t = peek(); } return expr; } Calculator parser - page 3 of 5 MulExpr : PrimaryExpr ( * PrimaryExpr | / PrimaryExpr )* Tuesday, September 3, 13
  60. function parseExpr() { var expr = parseMulExpr(); var t =

    peek(); while (t === "+" || t === "-") { consume(t); var rhs = parseMulExpr(); if (t === "+") expr = out.add(expr, rhs); else expr = out.sub(expr, rhs); t = peek(); } return expr; } Calculator parser - page 4 of 5 Expr : MulExpr ( + MulExpr | - MulExpr )* Tuesday, September 3, 13
  61. Calculator parser - page 5 of 5 var result =

    parseExpr(); if (position !== tokens.length) { throw new SyntaxError( "unexpected '" + peek() + "'"); } return result; } Tuesday, September 3, 13
  62. Calculator parser - page 5 of 5 var result =

    parseExpr(); if (position !== tokens.length) { throw new SyntaxError( "unexpected '" + peek() + "'"); } return result; } Tuesday, September 3, 13
  63. Calculator parser - page 5 of 5 var result =

    parseExpr(); if (position !== tokens.length) { throw new SyntaxError( "unexpected '" + peek() + "'"); } return result; } Tuesday, September 3, 13
  64. Calculator parser - page 5 of 5 var result =

    parseExpr(); if (position !== tokens.length) { throw new SyntaxError( "unexpected '" + peek() + "'"); } return result; } Tuesday, September 3, 13
  65. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement Tuesday, September 3, 13
  66. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement Tuesday, September 3, 13
  67. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement PrimaryExpr : Number Name ( Expr ) Tuesday, September 3, 13
  68. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement PrimaryExpr : Number Name ( Expr ) function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) { consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Tuesday, September 3, 13
  69. IfStatement : if ( Expression ) Statement else Statement if

    ( Expression ) Statement PrimaryExpr : Number Name ( Expr ) function parsePrimaryExpr() { var t = peek(); if (isNumber(t)) { consume(t); return out.number(t); } else if (isName(t)) { consume(t); return out.name(t); } else if (t === "(") { consume(t); var expr = parseExpr(); if (peek() !== ")") throw new SyntaxError("expected )"); consume(")"); return expr; } else { throw new SyntaxError("didn't expect '" + t + "'"); } } Tuesday, September 3, 13