[Ongoing] Rewrite frontend to use Flex/Bison

This is a merge of another experiment, so the changes are large:

- separated "modules" directory into frontend/backend
  - adjusted module names and moved files for this to happen
- removed modules lexer & parser
- removed all the unit tests (most were outdated)
- added Bison, flex, and C development tools to manifest.scm
- added lexer.l, a source file used by the flex utility with a functioning lexing implementation
- added parser.y, a source file used by the bison utility with a functioning parser implementation
- added node.c and node.h, which parser.y uses to construct an AST of a C source file (up to binary ops)
- added driver.c, a Guile-C interface that provides a module to scheme programs
- added a Makefile to make all of this
- added stuff to .gitignore

1 files changed, 116 insertions, 0 deletions

diff --git a/src/frontend/parser.y b/src/frontend/parser.y
new file mode 100644
index 0000000..aa58f64
--- /dev/null
+++ b/src/frontend/parser.y
@@ -0,0 +1,116 @@
+/*** definition section ***/
+%{
+  /* C to be copied verbatim */
+  #include "lexer.h"
+  #include "node.h"
+  void yyerror(Node **root, const char *msg);
+%}
+
+%code requires {
+  #include "node.h"
+}
+
+%union {
+  Node *node;
+  int ival;
+  char *sval;
+};
+
+%locations
+%start input
+%parse-param {Node **root}
+
+%token L_PAREN R_PAREN L_BRACK R_BRACK SEMI_COL COMP MULT DIV MOD MINUS PLUS INT VOID RET
+%token <sval> WORD
+%token <ival> NUMBER
+
+%type <node> input
+%type <node> func
+%type <node> stmt
+%type <node> exp
+%type <node> term
+%type <node> factor
+%type <ival> un_op
+
+
+/*** rules section ***/
+%%
+input:   func {
+    *root = create_node(PROG);
+    add_child(*root, $1);
+  }
+;
+
+func:   INT WORD L_PAREN VOID R_PAREN L_BRACK stmt R_BRACK {
+    $$ = create_function($2);
+    add_child($$, $7);
+  }
+;
+
+stmt:   RET exp SEMI_COL {
+    $$ = create_node(STMT);
+    add_child($$, $2);
+  }
+;
+
+exp:    term {
+    $$ = $1;
+  }
+|       exp PLUS term {
+    $$ = create_expr(PLUS_SYM);
+    add_child($$, $1);
+    add_child($$, $3);
+  }
+|       exp MINUS term {
+    $$ = create_expr(MINUS_SYM);
+    add_child($$, $1);
+    add_child($$, $3);
+  }
+|       un_op exp {
+    $$ = create_expr($1);
+    add_child($$, $2);
+  }
+;
+
+term:   factor {
+    $$ = $1;
+  }
+|       term MULT factor {
+    $$ = create_expr(MULT_SYM);
+    add_child($$, $1);
+    add_child($$, $3);
+  }
+|       term DIV factor {
+    $$ = create_expr(DIV_SYM);
+    add_child($$, $1);
+    add_child($$, $3);
+  }
+|       term MOD factor {
+    $$ = create_expr(MOD_SYM);
+    add_child($$, $1);
+    add_child($$, $3);
+  }
+;
+
+factor: NUMBER {
+    $$ = create_const($1);
+  }
+|       L_PAREN exp R_PAREN {
+    $$ = $2;
+  }
+;
+
+un_op:  COMP {
+    $$ = COMP_SYM;
+  }
+|       MINUS {
+    $$ = NEG_SYM;
+  }
+;
+
+%%
+
+void yyerror(Node **root, const char *msg) {
+  printf("** Line %d: %s\n", yylineno, msg);
+}
+