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1 // A Small Compiler for a Simple Functional Language |
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2 // (it does not include a parser and lexer) |
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3 |
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4 // abstract syntax trees |
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5 abstract class Exp |
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6 abstract class BExp |
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7 abstract class Decl |
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8 |
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9 // functions and declarations |
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10 case class Def(name: String, args: List[String], body: Exp) extends Decl |
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11 case class Main(e: Exp) extends Decl |
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12 |
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13 // expressions |
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14 case class Call(name: String, args: List[Exp]) extends Exp |
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15 case class If(a: BExp, e1: Exp, e2: Exp) extends Exp |
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16 case class Write(e: Exp) extends Exp |
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17 case class Var(s: String) extends Exp |
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18 case class Num(i: Int) extends Exp |
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19 case class Aop(o: String, a1: Exp, a2: Exp) extends Exp |
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20 case class Sequ(e1: Exp, e2: Exp) extends Exp |
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21 |
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22 // boolean expressions |
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23 case class Bop(o: String, a1: Exp, a2: Exp) extends BExp |
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24 |
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25 // calculating the maximal needed stack size |
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26 def max_stack_exp(e: Exp): Int = e match { |
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27 case Call(_, args) => args.map(max_stack_exp).sum |
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28 case If(a, e1, e2) => max_stack_bexp(a) + (List(max_stack_exp(e1), max_stack_exp(e2)).max) |
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29 case Write(e) => max_stack_exp(e) + 1 |
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30 case Var(_) => 1 |
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31 case Num(_) => 1 |
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32 case Aop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2) |
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33 case Sequ(e1, e2) => List(max_stack_exp(e1), max_stack_exp(e2)).max |
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34 } |
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35 def max_stack_bexp(e: BExp): Int = e match { |
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36 case Bop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2) |
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37 } |
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38 |
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39 // compiler - built-in functions |
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40 // copied from http://www.ceng.metu.edu.tr/courses/ceng444/link/jvm-cpm.html |
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41 // |
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42 |
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43 val library = """ |
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44 .class public XXX.XXX |
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45 .super java/lang/Object |
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46 |
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47 .method public static write(I)V |
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48 .limit locals 5 |
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49 .limit stack 5 |
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50 iload 0 |
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51 getstatic java/lang/System/out Ljava/io/PrintStream; |
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52 swap |
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53 invokevirtual java/io/PrintStream/println(I)V |
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54 return |
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55 .end method |
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56 |
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57 """ |
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58 |
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59 // for generating new labels |
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60 var counter = -1 |
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61 |
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62 def Fresh(x: String) = { |
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63 counter += 1 |
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64 x ++ "_" ++ counter.toString() |
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65 } |
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66 |
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67 // convenient string interpolations for |
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68 // generating instructions, labels etc |
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69 import scala.language.implicitConversions |
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70 import scala.language.reflectiveCalls |
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71 |
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72 // convenience for code-generation (string interpolations) |
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73 implicit def sring_inters(sc: StringContext) = new { |
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74 def i(args: Any*): String = " " ++ sc.s(args:_*) ++ "\n" // instructions |
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75 def l(args: Any*): String = sc.s(args:_*) ++ ":\n" // labels |
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76 def m(args: Any*): String = sc.s(args:_*) ++ "\n" // methods |
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77 } |
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78 |
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79 // variable / index environments |
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80 type Env = Map[String, Int] |
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81 |
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82 // compile expressions |
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83 def compile_exp(a: Exp, env : Env) : String = a match { |
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84 case Num(i) => i"ldc $i" |
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85 case Var(s) => i"iload ${env(s)}" |
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86 case Aop("+", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"iadd" |
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87 case Aop("-", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"isub" |
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88 case Aop("*", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"imul" |
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89 case Aop("/", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"idiv" |
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90 case Aop("%", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"irem" |
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91 case If(b, a1, a2) => { |
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92 val if_else = Fresh("If_else") |
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93 val if_end = Fresh("If_end") |
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94 compile_bexp(b, env, if_else) ++ |
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95 compile_exp(a1, env) ++ |
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96 i"goto $if_end" ++ |
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97 l"$if_else" ++ |
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98 compile_exp(a2, env) ++ |
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99 l"$if_end" |
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100 } |
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101 case Call(name, args) => { |
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102 val is = "I" * args.length |
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103 args.map(a => compile_exp(a, env)).mkString ++ |
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104 i"invokestatic XXX/XXX/$name($is)I" |
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105 } |
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106 case Sequ(a1, a2) => { |
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107 compile_exp(a1, env) ++ i"pop" ++ compile_exp(a2, env) |
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108 } |
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109 case Write(a1) => { |
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110 compile_exp(a1, env) ++ |
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111 i"dup" ++ |
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112 i"invokestatic XXX/XXX/write(I)V" |
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113 } |
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114 } |
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115 |
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116 // compile boolean expressions |
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117 def compile_bexp(b: BExp, env : Env, jmp: String) : String = b match { |
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118 case Bop("==", a1, a2) => |
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119 compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpne $jmp" |
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120 case Bop("!=", a1, a2) => |
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121 compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpeq $jmp" |
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122 case Bop("<", a1, a2) => |
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123 compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpge $jmp" |
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124 case Bop("<=", a1, a2) => |
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125 compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpgt $jmp" |
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126 } |
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127 |
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128 // compile functions and declarations |
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129 def compile_decl(d: Decl) : String = d match { |
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130 case Def(name, args, a) => { |
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131 val env = args.zipWithIndex.toMap |
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132 val is = "I" * args.length |
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133 m".method public static $name($is)I" ++ |
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134 m".limit locals ${args.length.toString}" ++ |
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135 m".limit stack ${1 + max_stack_exp(a)}" ++ |
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136 l"${name}_Start" ++ |
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137 compile_exp(a, env) ++ |
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138 i"ireturn" ++ |
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139 m".end method\n" |
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140 } |
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141 case Main(a) => { |
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142 m".method public static main([Ljava/lang/String;)V" ++ |
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143 m".limit locals 200" ++ |
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144 m".limit stack 200" ++ |
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145 compile_exp(a, Map()) ++ |
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146 i"invokestatic XXX/XXX/write(I)V" ++ |
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147 i"return" ++ |
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148 m".end method\n" |
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149 } |
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150 } |
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151 |
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152 // the main compilation function |
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153 def compile(prog: List[Decl], class_name: String) : String = { |
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154 val instructions = prog.map(compile_decl).mkString |
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155 (library + instructions).replaceAllLiterally("XXX", class_name) |
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156 } |
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157 |
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158 |
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159 |
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160 |
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161 // An example program (factorials) |
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162 // |
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163 // def fact(n) = if n == 0 then 1 else n * fact(n - 1); |
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164 // def facT(n, acc) = if n == 0 then acc else facT(n - 1, n * acc); |
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165 // |
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166 // fact(10) ; facT(15, 1) |
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167 // |
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168 |
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169 |
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170 val test_prog = |
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171 List(Def("fact", List("n"), |
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172 If(Bop("==",Var("n"),Num(0)), |
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173 Num(1), |
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174 Aop("*",Var("n"), |
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175 Call("fact",List(Aop("-",Var("n"),Num(1))))))), |
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176 |
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177 Def("facT",List("n", "acc"), |
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178 If(Bop("==",Var("n"),Num(0)), |
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179 Var("acc"), |
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180 Call("facT",List(Aop("-",Var("n"),Num(1)), |
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181 Aop("*",Var("n"),Var("acc")))))), |
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182 |
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183 Main(Sequ(Write(Call("fact",List(Num(10)))), |
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184 Write(Call("facT",List(Num(10), Num(1))))))) |
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185 |
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186 // prints out the JVM instructions |
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187 println(compile(test_prog, "fact")) |